1 /*
2 * Copyright (c) 2008, 2018, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.misc.SharedSecrets;
29 import jdk.internal.module.IllegalAccessLogger;
30 import jdk.internal.org.objectweb.asm.ClassReader;
31 import jdk.internal.reflect.CallerSensitive;
32 import jdk.internal.reflect.Reflection;
33 import jdk.internal.vm.annotation.ForceInline;
34 import sun.invoke.util.ValueConversions;
35 import sun.invoke.util.VerifyAccess;
36 import sun.invoke.util.Wrapper;
37 import sun.reflect.misc.ReflectUtil;
38 import sun.security.util.SecurityConstants;
39
40 import java.lang.invoke.LambdaForm.BasicType;
41 import java.lang.reflect.Constructor;
42 import java.lang.reflect.Field;
43 import java.lang.reflect.Member;
44 import java.lang.reflect.Method;
45 import java.lang.reflect.Modifier;
46 import java.lang.reflect.ReflectPermission;
47 import java.nio.ByteOrder;
48 import java.security.AccessController;
49 import java.security.PrivilegedAction;
50 import java.security.ProtectionDomain;
51 import java.util.ArrayList;
52 import java.util.Arrays;
53 import java.util.BitSet;
54 import java.util.Iterator;
55 import java.util.List;
56 import java.util.Objects;
57 import java.util.concurrent.ConcurrentHashMap;
58 import java.util.stream.Collectors;
59 import java.util.stream.Stream;
60
61 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
62 import static java.lang.invoke.MethodHandleNatives.Constants.*;
63 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
64 import static java.lang.invoke.MethodType.methodType;
65
66 /**
67 * This class consists exclusively of static methods that operate on or return
68 * method handles. They fall into several categories:
69 * <ul>
70 * <li>Lookup methods which help create method handles for methods and fields.
71 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
72 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
73 * </ul>
74 *
75 * @author John Rose, JSR 292 EG
76 * @since 1.7
77 */
78 public class MethodHandles {
79
80 private MethodHandles() { } // do not instantiate
81
82 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
83
84 // See IMPL_LOOKUP below.
85
86 //// Method handle creation from ordinary methods.
87
88 /**
89 * Returns a {@link Lookup lookup object} with
90 * full capabilities to emulate all supported bytecode behaviors of the caller.
91 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
92 * Factory methods on the lookup object can create
93 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
94 * for any member that the caller has access to via bytecodes,
95 * including protected and private fields and methods.
96 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
97 * Do not store it in place where untrusted code can access it.
98 * <p>
99 * This method is caller sensitive, which means that it may return different
100 * values to different callers.
101 * @return a lookup object for the caller of this method, with private access
102 */
103 @CallerSensitive
104 @ForceInline // to ensure Reflection.getCallerClass optimization
105 public static Lookup lookup() {
106 return new Lookup(Reflection.getCallerClass());
107 }
108
109 /**
110 * This reflected$lookup method is the alternate implementation of
111 * the lookup method when being invoked by reflection.
112 */
113 @CallerSensitive
114 private static Lookup reflected$lookup() {
115 Class<?> caller = Reflection.getCallerClass();
116 if (caller.getClassLoader() == null) {
117 throw newIllegalArgumentException("illegal lookupClass: "+caller);
118 }
119 return new Lookup(caller);
120 }
121
122 /**
123 * Returns a {@link Lookup lookup object} which is trusted minimally.
124 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
125 * It can only be used to create method handles to public members of
126 * public classes in packages that are exported unconditionally.
127 * <p>
128 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
129 * of this lookup object will be {@link java.lang.Object}.
130 *
131 * @apiNote The use of Object is conventional, and because the lookup modes are
132 * limited, there is no special access provided to the internals of Object, its package
133 * or its module. Consequently, the lookup context of this lookup object will be the
134 * bootstrap class loader, which means it cannot find user classes.
135 *
136 * <p style="font-size:smaller;">
137 * <em>Discussion:</em>
138 * The lookup class can be changed to any other class {@code C} using an expression of the form
139 * {@link Lookup#in publicLookup().in(C.class)}.
140 * but may change the lookup context by virtue of changing the class loader.
141 * A public lookup object is always subject to
142 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
143 * Also, it cannot access
144 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
145 * @return a lookup object which is trusted minimally
146 *
147 * @revised 9
148 * @spec JPMS
149 */
150 public static Lookup publicLookup() {
151 return Lookup.PUBLIC_LOOKUP;
152 }
153
154 /**
155 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
156 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
157 * private access</a>, on a target class.
158 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
159 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
160 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
161 * the target class, then this check ensures that
162 * <ul>
163 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
164 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
165 * the target class to at least {@code m1}.</li>
166 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
167 * </ul>
168 * <p>
169 * If there is a security manager, its {@code checkPermission} method is called to
170 * check {@code ReflectPermission("suppressAccessChecks")}.
171 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
172 * was created by code in the caller module (or derived from a lookup object originally
173 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
174 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
175 * access to the caller.
176 * @param targetClass the target class
177 * @param lookup the caller lookup object
178 * @return a lookup object for the target class, with private access
179 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class
180 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
181 * @throws IllegalAccessException if the access check specified above fails
182 * @throws SecurityException if denied by the security manager
183 * @since 9
184 * @spec JPMS
185 * @see Lookup#dropLookupMode
186 */
187 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
188 SecurityManager sm = System.getSecurityManager();
189 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
190 if (targetClass.isPrimitive())
191 throw new IllegalArgumentException(targetClass + " is a primitive class");
192 if (targetClass.isArray())
193 throw new IllegalArgumentException(targetClass + " is an array class");
194 Module targetModule = targetClass.getModule();
195 Module callerModule = lookup.lookupClass().getModule();
196 if (!callerModule.canRead(targetModule))
197 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
198 if (targetModule.isNamed()) {
199 String pn = targetClass.getPackageName();
200 assert !pn.isEmpty() : "unnamed package cannot be in named module";
201 if (!targetModule.isOpen(pn, callerModule))
202 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
203 }
204 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
205 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
206 if (!callerModule.isNamed() && targetModule.isNamed()) {
207 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
208 if (logger != null) {
209 logger.logIfOpenedForIllegalAccess(lookup, targetClass);
210 }
211 }
212 return new Lookup(targetClass);
213 }
214
215 /**
216 * Performs an unchecked "crack" of a
217 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
218 * The result is as if the user had obtained a lookup object capable enough
219 * to crack the target method handle, called
220 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
221 * on the target to obtain its symbolic reference, and then called
222 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
223 * to resolve the symbolic reference to a member.
224 * <p>
225 * If there is a security manager, its {@code checkPermission} method
226 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
227 * @param <T> the desired type of the result, either {@link Member} or a subtype
228 * @param target a direct method handle to crack into symbolic reference components
229 * @param expected a class object representing the desired result type {@code T}
230 * @return a reference to the method, constructor, or field object
231 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
232 * @exception NullPointerException if either argument is {@code null}
233 * @exception IllegalArgumentException if the target is not a direct method handle
234 * @exception ClassCastException if the member is not of the expected type
235 * @since 1.8
236 */
237 public static <T extends Member> T
238 reflectAs(Class<T> expected, MethodHandle target) {
239 SecurityManager smgr = System.getSecurityManager();
240 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
241 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
242 return lookup.revealDirect(target).reflectAs(expected, lookup);
243 }
244 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
245 private static final java.security.Permission ACCESS_PERMISSION =
246 new ReflectPermission("suppressAccessChecks");
247
248 /**
249 * A <em>lookup object</em> is a factory for creating method handles,
250 * when the creation requires access checking.
251 * Method handles do not perform
252 * access checks when they are called, but rather when they are created.
253 * Therefore, method handle access
254 * restrictions must be enforced when a method handle is created.
255 * The caller class against which those restrictions are enforced
256 * is known as the {@linkplain #lookupClass() lookup class}.
257 * <p>
258 * A lookup class which needs to create method handles will call
259 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
260 * When the {@code Lookup} factory object is created, the identity of the lookup class is
261 * determined, and securely stored in the {@code Lookup} object.
262 * The lookup class (or its delegates) may then use factory methods
263 * on the {@code Lookup} object to create method handles for access-checked members.
264 * This includes all methods, constructors, and fields which are allowed to the lookup class,
265 * even private ones.
266 *
267 * <h1><a id="lookups"></a>Lookup Factory Methods</h1>
268 * The factory methods on a {@code Lookup} object correspond to all major
269 * use cases for methods, constructors, and fields.
270 * Each method handle created by a factory method is the functional
271 * equivalent of a particular <em>bytecode behavior</em>.
272 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
273 * Here is a summary of the correspondence between these factory methods and
274 * the behavior of the resulting method handles:
275 * <table class="striped">
276 * <caption style="display:none">lookup method behaviors</caption>
277 * <thead>
278 * <tr>
279 * <th scope="col"><a id="equiv"></a>lookup expression</th>
280 * <th scope="col">member</th>
281 * <th scope="col">bytecode behavior</th>
282 * </tr>
283 * </thead>
284 * <tbody>
285 * <tr>
286 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
287 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
288 * </tr>
289 * <tr>
290 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
291 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
292 * </tr>
293 * <tr>
294 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
295 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
296 * </tr>
297 * <tr>
298 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
299 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
300 * </tr>
301 * <tr>
302 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
303 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
304 * </tr>
305 * <tr>
306 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
307 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
308 * </tr>
309 * <tr>
310 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
311 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
312 * </tr>
313 * <tr>
314 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
315 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
316 * </tr>
317 * <tr>
318 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
319 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
320 * </tr>
321 * <tr>
322 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
323 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
324 * </tr>
325 * <tr>
326 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
327 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
328 * </tr>
329 * <tr>
330 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
331 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
332 * </tr>
333 * <tr>
334 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
335 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
336 * </tr>
337 * <tr>
338 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
339 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
340 * </tr>
341 * </tbody>
342 * </table>
343 *
344 * Here, the type {@code C} is the class or interface being searched for a member,
345 * documented as a parameter named {@code refc} in the lookup methods.
346 * The method type {@code MT} is composed from the return type {@code T}
347 * and the sequence of argument types {@code A*}.
348 * The constructor also has a sequence of argument types {@code A*} and
349 * is deemed to return the newly-created object of type {@code C}.
350 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
351 * The formal parameter {@code this} stands for the self-reference of type {@code C};
352 * if it is present, it is always the leading argument to the method handle invocation.
353 * (In the case of some {@code protected} members, {@code this} may be
354 * restricted in type to the lookup class; see below.)
355 * The name {@code arg} stands for all the other method handle arguments.
356 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
357 * stands for a null reference if the accessed method or field is static,
358 * and {@code this} otherwise.
359 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
360 * for reflective objects corresponding to the given members.
361 * <p>
362 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
363 * as if by {@code ldc CONSTANT_Class}.
364 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
365 * <p>
366 * In cases where the given member is of variable arity (i.e., a method or constructor)
367 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
368 * In all other cases, the returned method handle will be of fixed arity.
369 * <p style="font-size:smaller;">
370 * <em>Discussion:</em>
371 * The equivalence between looked-up method handles and underlying
372 * class members and bytecode behaviors
373 * can break down in a few ways:
374 * <ul style="font-size:smaller;">
375 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
376 * the lookup can still succeed, even when there is no equivalent
377 * Java expression or bytecoded constant.
378 * <li>Likewise, if {@code T} or {@code MT}
379 * is not symbolically accessible from the lookup class's loader,
380 * the lookup can still succeed.
381 * For example, lookups for {@code MethodHandle.invokeExact} and
382 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
383 * <li>If there is a security manager installed, it can forbid the lookup
384 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
385 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
386 * constant is not subject to security manager checks.
387 * <li>If the looked-up method has a
388 * <a href="MethodHandle.html#maxarity">very large arity</a>,
389 * the method handle creation may fail, due to the method handle
390 * type having too many parameters.
391 * </ul>
392 *
393 * <h1><a id="access"></a>Access checking</h1>
394 * Access checks are applied in the factory methods of {@code Lookup},
395 * when a method handle is created.
396 * This is a key difference from the Core Reflection API, since
397 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
398 * performs access checking against every caller, on every call.
399 * <p>
400 * All access checks start from a {@code Lookup} object, which
401 * compares its recorded lookup class against all requests to
402 * create method handles.
403 * A single {@code Lookup} object can be used to create any number
404 * of access-checked method handles, all checked against a single
405 * lookup class.
406 * <p>
407 * A {@code Lookup} object can be shared with other trusted code,
408 * such as a metaobject protocol.
409 * A shared {@code Lookup} object delegates the capability
410 * to create method handles on private members of the lookup class.
411 * Even if privileged code uses the {@code Lookup} object,
412 * the access checking is confined to the privileges of the
413 * original lookup class.
414 * <p>
415 * A lookup can fail, because
416 * the containing class is not accessible to the lookup class, or
417 * because the desired class member is missing, or because the
418 * desired class member is not accessible to the lookup class, or
419 * because the lookup object is not trusted enough to access the member.
420 * In any of these cases, a {@code ReflectiveOperationException} will be
421 * thrown from the attempted lookup. The exact class will be one of
422 * the following:
423 * <ul>
424 * <li>NoSuchMethodException — if a method is requested but does not exist
425 * <li>NoSuchFieldException — if a field is requested but does not exist
426 * <li>IllegalAccessException — if the member exists but an access check fails
427 * </ul>
428 * <p>
429 * In general, the conditions under which a method handle may be
430 * looked up for a method {@code M} are no more restrictive than the conditions
431 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
432 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
433 * a method handle lookup will generally raise a corresponding
434 * checked exception, such as {@code NoSuchMethodException}.
435 * And the effect of invoking the method handle resulting from the lookup
436 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
437 * to executing the compiled, verified, and resolved call to {@code M}.
438 * The same point is true of fields and constructors.
439 * <p style="font-size:smaller;">
440 * <em>Discussion:</em>
441 * Access checks only apply to named and reflected methods,
442 * constructors, and fields.
443 * Other method handle creation methods, such as
444 * {@link MethodHandle#asType MethodHandle.asType},
445 * do not require any access checks, and are used
446 * independently of any {@code Lookup} object.
447 * <p>
448 * If the desired member is {@code protected}, the usual JVM rules apply,
449 * including the requirement that the lookup class must be either be in the
450 * same package as the desired member, or must inherit that member.
451 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
452 * In addition, if the desired member is a non-static field or method
453 * in a different package, the resulting method handle may only be applied
454 * to objects of the lookup class or one of its subclasses.
455 * This requirement is enforced by narrowing the type of the leading
456 * {@code this} parameter from {@code C}
457 * (which will necessarily be a superclass of the lookup class)
458 * to the lookup class itself.
459 * <p>
460 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
461 * that the receiver argument must match both the resolved method <em>and</em>
462 * the current class. Again, this requirement is enforced by narrowing the
463 * type of the leading parameter to the resulting method handle.
464 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
465 * <p>
466 * The JVM represents constructors and static initializer blocks as internal methods
467 * with special names ({@code "<init>"} and {@code "<clinit>"}).
468 * The internal syntax of invocation instructions allows them to refer to such internal
469 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
470 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
471 * <p>
472 * If the relationship between nested types is expressed directly through the
473 * {@code NestHost} and {@code NestMembers} attributes
474 * (see the Java Virtual Machine Specification, sections 4.7.28 and 4.7.29),
475 * then the associated {@code Lookup} object provides direct access to
476 * the lookup class and all of its nestmates
477 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
478 * Otherwise, access between nested classes is obtained by the Java compiler creating
479 * a wrapper method to access a private method of another class in the same nest.
480 * For example, a nested class {@code C.D}
481 * can access private members within other related classes such as
482 * {@code C}, {@code C.D.E}, or {@code C.B},
483 * but the Java compiler may need to generate wrapper methods in
484 * those related classes. In such cases, a {@code Lookup} object on
485 * {@code C.E} would be unable to access those private members.
486 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
487 * which can transform a lookup on {@code C.E} into one on any of those other
488 * classes, without special elevation of privilege.
489 * <p>
490 * The accesses permitted to a given lookup object may be limited,
491 * according to its set of {@link #lookupModes lookupModes},
492 * to a subset of members normally accessible to the lookup class.
493 * For example, the {@link MethodHandles#publicLookup publicLookup}
494 * method produces a lookup object which is only allowed to access
495 * public members in public classes of exported packages.
496 * The caller sensitive method {@link MethodHandles#lookup lookup}
497 * produces a lookup object with full capabilities relative to
498 * its caller class, to emulate all supported bytecode behaviors.
499 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
500 * with fewer access modes than the original lookup object.
501 *
502 * <p style="font-size:smaller;">
503 * <a id="privacc"></a>
504 * <em>Discussion of private access:</em>
505 * We say that a lookup has <em>private access</em>
506 * if its {@linkplain #lookupModes lookup modes}
507 * include the possibility of accessing {@code private} members
508 * (which includes the private members of nestmates).
509 * As documented in the relevant methods elsewhere,
510 * only lookups with private access possess the following capabilities:
511 * <ul style="font-size:smaller;">
512 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
513 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
514 * such as {@code Class.forName}
515 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
516 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
517 * for classes accessible to the lookup class
518 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
519 * within the same package member
520 * </ul>
521 * <p style="font-size:smaller;">
522 * Each of these permissions is a consequence of the fact that a lookup object
523 * with private access can be securely traced back to an originating class,
524 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
525 * can be reliably determined and emulated by method handles.
526 *
527 * <h1><a id="secmgr"></a>Security manager interactions</h1>
528 * Although bytecode instructions can only refer to classes in
529 * a related class loader, this API can search for methods in any
530 * class, as long as a reference to its {@code Class} object is
531 * available. Such cross-loader references are also possible with the
532 * Core Reflection API, and are impossible to bytecode instructions
533 * such as {@code invokestatic} or {@code getfield}.
534 * There is a {@linkplain java.lang.SecurityManager security manager API}
535 * to allow applications to check such cross-loader references.
536 * These checks apply to both the {@code MethodHandles.Lookup} API
537 * and the Core Reflection API
538 * (as found on {@link java.lang.Class Class}).
539 * <p>
540 * If a security manager is present, member and class lookups are subject to
541 * additional checks.
542 * From one to three calls are made to the security manager.
543 * Any of these calls can refuse access by throwing a
544 * {@link java.lang.SecurityException SecurityException}.
545 * Define {@code smgr} as the security manager,
546 * {@code lookc} as the lookup class of the current lookup object,
547 * {@code refc} as the containing class in which the member
548 * is being sought, and {@code defc} as the class in which the
549 * member is actually defined.
550 * (If a class or other type is being accessed,
551 * the {@code refc} and {@code defc} values are the class itself.)
552 * The value {@code lookc} is defined as <em>not present</em>
553 * if the current lookup object does not have
554 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
555 * The calls are made according to the following rules:
556 * <ul>
557 * <li><b>Step 1:</b>
558 * If {@code lookc} is not present, or if its class loader is not
559 * the same as or an ancestor of the class loader of {@code refc},
560 * then {@link SecurityManager#checkPackageAccess
561 * smgr.checkPackageAccess(refcPkg)} is called,
562 * where {@code refcPkg} is the package of {@code refc}.
563 * <li><b>Step 2a:</b>
564 * If the retrieved member is not public and
565 * {@code lookc} is not present, then
566 * {@link SecurityManager#checkPermission smgr.checkPermission}
567 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
568 * <li><b>Step 2b:</b>
569 * If the retrieved class has a {@code null} class loader,
570 * and {@code lookc} is not present, then
571 * {@link SecurityManager#checkPermission smgr.checkPermission}
572 * with {@code RuntimePermission("getClassLoader")} is called.
573 * <li><b>Step 3:</b>
574 * If the retrieved member is not public,
575 * and if {@code lookc} is not present,
576 * and if {@code defc} and {@code refc} are different,
577 * then {@link SecurityManager#checkPackageAccess
578 * smgr.checkPackageAccess(defcPkg)} is called,
579 * where {@code defcPkg} is the package of {@code defc}.
580 * </ul>
581 * Security checks are performed after other access checks have passed.
582 * Therefore, the above rules presuppose a member or class that is public,
583 * or else that is being accessed from a lookup class that has
584 * rights to access the member or class.
585 *
586 * <h1><a id="callsens"></a>Caller sensitive methods</h1>
587 * A small number of Java methods have a special property called caller sensitivity.
588 * A <em>caller-sensitive</em> method can behave differently depending on the
589 * identity of its immediate caller.
590 * <p>
591 * If a method handle for a caller-sensitive method is requested,
592 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
593 * but they take account of the lookup class in a special way.
594 * The resulting method handle behaves as if it were called
595 * from an instruction contained in the lookup class,
596 * so that the caller-sensitive method detects the lookup class.
597 * (By contrast, the invoker of the method handle is disregarded.)
598 * Thus, in the case of caller-sensitive methods,
599 * different lookup classes may give rise to
600 * differently behaving method handles.
601 * <p>
602 * In cases where the lookup object is
603 * {@link MethodHandles#publicLookup() publicLookup()},
604 * or some other lookup object without
605 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
606 * the lookup class is disregarded.
607 * In such cases, no caller-sensitive method handle can be created,
608 * access is forbidden, and the lookup fails with an
609 * {@code IllegalAccessException}.
610 * <p style="font-size:smaller;">
611 * <em>Discussion:</em>
612 * For example, the caller-sensitive method
613 * {@link java.lang.Class#forName(String) Class.forName(x)}
614 * can return varying classes or throw varying exceptions,
615 * depending on the class loader of the class that calls it.
616 * A public lookup of {@code Class.forName} will fail, because
617 * there is no reasonable way to determine its bytecode behavior.
618 * <p style="font-size:smaller;">
619 * If an application caches method handles for broad sharing,
620 * it should use {@code publicLookup()} to create them.
621 * If there is a lookup of {@code Class.forName}, it will fail,
622 * and the application must take appropriate action in that case.
623 * It may be that a later lookup, perhaps during the invocation of a
624 * bootstrap method, can incorporate the specific identity
625 * of the caller, making the method accessible.
626 * <p style="font-size:smaller;">
627 * The function {@code MethodHandles.lookup} is caller sensitive
628 * so that there can be a secure foundation for lookups.
629 * Nearly all other methods in the JSR 292 API rely on lookup
630 * objects to check access requests.
631 *
632 * @revised 9
633 */
634 public static final
635 class Lookup {
636 /** The class on behalf of whom the lookup is being performed. */
637 private final Class<?> lookupClass;
638
639 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
640 private final int allowedModes;
641
642 /** A single-bit mask representing {@code public} access,
643 * which may contribute to the result of {@link #lookupModes lookupModes}.
644 * The value, {@code 0x01}, happens to be the same as the value of the
645 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
646 */
647 public static final int PUBLIC = Modifier.PUBLIC;
648
649 /** A single-bit mask representing {@code private} access,
650 * which may contribute to the result of {@link #lookupModes lookupModes}.
651 * The value, {@code 0x02}, happens to be the same as the value of the
652 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
653 */
654 public static final int PRIVATE = Modifier.PRIVATE;
655
656 /** A single-bit mask representing {@code protected} access,
657 * which may contribute to the result of {@link #lookupModes lookupModes}.
658 * The value, {@code 0x04}, happens to be the same as the value of the
659 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
660 */
661 public static final int PROTECTED = Modifier.PROTECTED;
662
663 /** A single-bit mask representing {@code package} access (default access),
664 * which may contribute to the result of {@link #lookupModes lookupModes}.
665 * The value is {@code 0x08}, which does not correspond meaningfully to
666 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
667 */
668 public static final int PACKAGE = Modifier.STATIC;
669
670 /** A single-bit mask representing {@code module} access (default access),
671 * which may contribute to the result of {@link #lookupModes lookupModes}.
672 * The value is {@code 0x10}, which does not correspond meaningfully to
673 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
674 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
675 * with this lookup mode can access all public types in the module of the
676 * lookup class and public types in packages exported by other modules
677 * to the module of the lookup class.
678 * @since 9
679 * @spec JPMS
680 */
681 public static final int MODULE = PACKAGE << 1;
682
683 /** A single-bit mask representing {@code unconditional} access
684 * which may contribute to the result of {@link #lookupModes lookupModes}.
685 * The value is {@code 0x20}, which does not correspond meaningfully to
686 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
687 * A {@code Lookup} with this lookup mode assumes {@linkplain
688 * java.lang.Module#canRead(java.lang.Module) readability}.
689 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
690 * with this lookup mode can access all public members of public types
691 * of all modules where the type is in a package that is {@link
692 * java.lang.Module#isExported(String) exported unconditionally}.
693 * @since 9
694 * @spec JPMS
695 * @see #publicLookup()
696 */
697 public static final int UNCONDITIONAL = PACKAGE << 2;
698
699 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
700 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
701 private static final int TRUSTED = -1;
702
703 private static int fixmods(int mods) {
704 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
705 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
706 }
707
708 /** Tells which class is performing the lookup. It is this class against
709 * which checks are performed for visibility and access permissions.
710 * <p>
711 * The class implies a maximum level of access permission,
712 * but the permissions may be additionally limited by the bitmask
713 * {@link #lookupModes lookupModes}, which controls whether non-public members
714 * can be accessed.
715 * @return the lookup class, on behalf of which this lookup object finds members
716 */
717 public Class<?> lookupClass() {
718 return lookupClass;
719 }
720
721 // This is just for calling out to MethodHandleImpl.
722 private Class<?> lookupClassOrNull() {
723 return (allowedModes == TRUSTED) ? null : lookupClass;
724 }
725
726 /** Tells which access-protection classes of members this lookup object can produce.
727 * The result is a bit-mask of the bits
728 * {@linkplain #PUBLIC PUBLIC (0x01)},
729 * {@linkplain #PRIVATE PRIVATE (0x02)},
730 * {@linkplain #PROTECTED PROTECTED (0x04)},
731 * {@linkplain #PACKAGE PACKAGE (0x08)},
732 * {@linkplain #MODULE MODULE (0x10)},
733 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
734 * <p>
735 * A freshly-created lookup object
736 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
737 * all possible bits set, except {@code UNCONDITIONAL}.
738 * A lookup object on a new lookup class
739 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
740 * may have some mode bits set to zero.
741 * Mode bits can also be
742 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
743 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
744 * The purpose of this is to restrict access via the new lookup object,
745 * so that it can access only names which can be reached by the original
746 * lookup object, and also by the new lookup class.
747 * @return the lookup modes, which limit the kinds of access performed by this lookup object
748 * @see #in
749 * @see #dropLookupMode
750 *
751 * @revised 9
752 * @spec JPMS
753 */
754 public int lookupModes() {
755 return allowedModes & ALL_MODES;
756 }
757
758 /** Embody the current class (the lookupClass) as a lookup class
759 * for method handle creation.
760 * Must be called by from a method in this package,
761 * which in turn is called by a method not in this package.
762 */
763 Lookup(Class<?> lookupClass) {
764 this(lookupClass, FULL_POWER_MODES);
765 // make sure we haven't accidentally picked up a privileged class:
766 checkUnprivilegedlookupClass(lookupClass);
767 }
768
769 private Lookup(Class<?> lookupClass, int allowedModes) {
770 this.lookupClass = lookupClass;
771 this.allowedModes = allowedModes;
772 }
773
774 /**
775 * Creates a lookup on the specified new lookup class.
776 * The resulting object will report the specified
777 * class as its own {@link #lookupClass() lookupClass}.
778 * <p>
779 * However, the resulting {@code Lookup} object is guaranteed
780 * to have no more access capabilities than the original.
781 * In particular, access capabilities can be lost as follows:<ul>
782 * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and
783 * the new lookup class is in a different module {@code M}, then no members, not
784 * even public members in {@code M}'s exported packages, will be accessible.
785 * The exception to this is when this lookup is {@link #publicLookup()
786 * publicLookup}, in which case {@code PUBLIC} access is not lost.
787 * <li>If the old lookup class is in an unnamed module, and the new lookup class
788 * is a different module then {@link #MODULE MODULE} access is lost.
789 * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost.
790 * <li>If the new lookup class is in a different package
791 * than the old one, protected and default (package) members will not be accessible.
792 * <li>If the new lookup class is not within the same package member
793 * as the old one, private members will not be accessible, and protected members
794 * will not be accessible by virtue of inheritance.
795 * (Protected members may continue to be accessible because of package sharing.)
796 * <li>If the new lookup class is not accessible to the old lookup class,
797 * then no members, not even public members, will be accessible.
798 * (In all other cases, public members will continue to be accessible.)
799 * </ul>
800 * <p>
801 * The resulting lookup's capabilities for loading classes
802 * (used during {@link #findClass} invocations)
803 * are determined by the lookup class' loader,
804 * which may change due to this operation.
805 *
806 * @param requestedLookupClass the desired lookup class for the new lookup object
807 * @return a lookup object which reports the desired lookup class, or the same object
808 * if there is no change
809 * @throws NullPointerException if the argument is null
810 *
811 * @revised 9
812 * @spec JPMS
813 */
814 public Lookup in(Class<?> requestedLookupClass) {
815 Objects.requireNonNull(requestedLookupClass);
816 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
817 return new Lookup(requestedLookupClass, FULL_POWER_MODES);
818 if (requestedLookupClass == this.lookupClass)
819 return this; // keep same capabilities
820 int newModes = (allowedModes & FULL_POWER_MODES);
821 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
822 // Need to drop all access when teleporting from a named module to another
823 // module. The exception is publicLookup where PUBLIC is not lost.
824 if (this.lookupClass.getModule().isNamed()
825 && (this.allowedModes & UNCONDITIONAL) == 0)
826 newModes = 0;
827 else
828 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
829 }
830 if ((newModes & PACKAGE) != 0
831 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
832 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
833 }
834 // Allow nestmate lookups to be created without special privilege:
835 if ((newModes & PRIVATE) != 0
836 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
837 newModes &= ~(PRIVATE|PROTECTED);
838 }
839 if ((newModes & PUBLIC) != 0
840 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
841 // The requested class it not accessible from the lookup class.
842 // No permissions.
843 newModes = 0;
844 }
845
846 checkUnprivilegedlookupClass(requestedLookupClass);
847 return new Lookup(requestedLookupClass, newModes);
848 }
849
850
851 /**
852 * Creates a lookup on the same lookup class which this lookup object
853 * finds members, but with a lookup mode that has lost the given lookup mode.
854 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
855 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
856 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
857 * dropped and so the resulting lookup mode will never have these access capabilities.
858 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
859 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
860 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
861 * is dropped then the resulting lookup has no access.
862 * @param modeToDrop the lookup mode to drop
863 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
864 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
865 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
866 * @see MethodHandles#privateLookupIn
867 * @since 9
868 */
869 public Lookup dropLookupMode(int modeToDrop) {
870 int oldModes = lookupModes();
871 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
872 switch (modeToDrop) {
873 case PUBLIC: newModes &= ~(ALL_MODES); break;
874 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
875 case PACKAGE: newModes &= ~(PRIVATE); break;
876 case PROTECTED:
877 case PRIVATE:
878 case UNCONDITIONAL: break;
879 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
880 }
881 if (newModes == oldModes) return this; // return self if no change
882 return new Lookup(lookupClass(), newModes);
883 }
884
885 /**
886 * Defines a class to the same class loader and in the same runtime package and
887 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
888 * {@linkplain #lookupClass() lookup class}.
889 *
890 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
891 * {@link #PACKAGE PACKAGE} access as default (package) members will be
892 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
893 * that the lookup object was created by a caller in the runtime package (or derived
894 * from a lookup originally created by suitably privileged code to a target class in
895 * the runtime package). </p>
896 *
897 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
898 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
899 * same package as the lookup class. </p>
900 *
901 * <p> This method does not run the class initializer. The class initializer may
902 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
903 * Specification</em>. </p>
904 *
905 * <p> If there is a security manager, its {@code checkPermission} method is first called
906 * to check {@code RuntimePermission("defineClass")}. </p>
907 *
908 * @param bytes the class bytes
909 * @return the {@code Class} object for the class
910 * @throws IllegalArgumentException the bytes are for a class in a different package
911 * to the lookup class
912 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
913 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
914 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
915 * @throws SecurityException if denied by the security manager
916 * @throws NullPointerException if {@code bytes} is {@code null}
917 * @since 9
918 * @spec JPMS
919 * @see Lookup#privateLookupIn
920 * @see Lookup#dropLookupMode
921 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
922 */
923 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
924 SecurityManager sm = System.getSecurityManager();
925 if (sm != null)
926 sm.checkPermission(new RuntimePermission("defineClass"));
927 if ((lookupModes() & PACKAGE) == 0)
928 throw new IllegalAccessException("Lookup does not have PACKAGE access");
929 assert (lookupModes() & (MODULE|PUBLIC)) != 0;
930
931 // parse class bytes to get class name (in internal form)
932 bytes = bytes.clone();
933 String name;
934 try {
935 ClassReader reader = new ClassReader(bytes);
936 name = reader.getClassName();
937 } catch (RuntimeException e) {
938 // ASM exceptions are poorly specified
939 ClassFormatError cfe = new ClassFormatError();
940 cfe.initCause(e);
941 throw cfe;
942 }
943
944 // get package and class name in binary form
945 String cn, pn;
946 int index = name.lastIndexOf('/');
947 if (index == -1) {
948 cn = name;
949 pn = "";
950 } else {
951 cn = name.replace('/', '.');
952 pn = cn.substring(0, index);
953 }
954 if (!pn.equals(lookupClass.getPackageName())) {
955 throw new IllegalArgumentException("Class not in same package as lookup class");
956 }
957
958 // invoke the class loader's defineClass method
959 ClassLoader loader = lookupClass.getClassLoader();
960 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
961 String source = "__Lookup_defineClass__";
962 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);
963 assert clazz.getClassLoader() == lookupClass.getClassLoader()
964 && clazz.getPackageName().equals(lookupClass.getPackageName())
965 && protectionDomain(clazz) == lookupClassProtectionDomain();
966 return clazz;
967 }
968
969 private ProtectionDomain lookupClassProtectionDomain() {
970 ProtectionDomain pd = cachedProtectionDomain;
971 if (pd == null) {
972 cachedProtectionDomain = pd = protectionDomain(lookupClass);
973 }
974 return pd;
975 }
976
977 private ProtectionDomain protectionDomain(Class<?> clazz) {
978 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
979 return AccessController.doPrivileged(pa);
980 }
981
982 // cached protection domain
983 private volatile ProtectionDomain cachedProtectionDomain;
984
985
986 // Make sure outer class is initialized first.
987 static { IMPL_NAMES.getClass(); }
988
989 /** Package-private version of lookup which is trusted. */
990 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
991
992 /** Version of lookup which is trusted minimally.
993 * It can only be used to create method handles to publicly accessible
994 * members in packages that are exported unconditionally.
995 */
996 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
997
998 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
999 String name = lookupClass.getName();
1000 if (name.startsWith("java.lang.invoke."))
1001 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1002 }
1003
1004 /**
1005 * Displays the name of the class from which lookups are to be made.
1006 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1007 * If there are restrictions on the access permitted to this lookup,
1008 * this is indicated by adding a suffix to the class name, consisting
1009 * of a slash and a keyword. The keyword represents the strongest
1010 * allowed access, and is chosen as follows:
1011 * <ul>
1012 * <li>If no access is allowed, the suffix is "/noaccess".
1013 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1014 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
1015 * <li>If only public and module access are allowed, the suffix is "/module".
1016 * <li>If only public, module and package access are allowed, the suffix is "/package".
1017 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
1018 * </ul>
1019 * If none of the above cases apply, it is the case that full
1020 * access (public, module, package, private, and protected) is allowed.
1021 * In this case, no suffix is added.
1022 * This is true only of an object obtained originally from
1023 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1024 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1025 * always have restricted access, and will display a suffix.
1026 * <p>
1027 * (It may seem strange that protected access should be
1028 * stronger than private access. Viewed independently from
1029 * package access, protected access is the first to be lost,
1030 * because it requires a direct subclass relationship between
1031 * caller and callee.)
1032 * @see #in
1033 *
1034 * @revised 9
1035 * @spec JPMS
1036 */
1037 @Override
1038 public String toString() {
1039 String cname = lookupClass.getName();
1040 switch (allowedModes) {
1041 case 0: // no privileges
1042 return cname + "/noaccess";
1043 case PUBLIC:
1044 return cname + "/public";
1045 case PUBLIC|UNCONDITIONAL:
1046 return cname + "/publicLookup";
1047 case PUBLIC|MODULE:
1048 return cname + "/module";
1049 case PUBLIC|MODULE|PACKAGE:
1050 return cname + "/package";
1051 case FULL_POWER_MODES & ~PROTECTED:
1052 return cname + "/private";
1053 case FULL_POWER_MODES:
1054 return cname;
1055 case TRUSTED:
1056 return "/trusted"; // internal only; not exported
1057 default: // Should not happen, but it's a bitfield...
1058 cname = cname + "/" + Integer.toHexString(allowedModes);
1059 assert(false) : cname;
1060 return cname;
1061 }
1062 }
1063
1064 /**
1065 * Produces a method handle for a static method.
1066 * The type of the method handle will be that of the method.
1067 * (Since static methods do not take receivers, there is no
1068 * additional receiver argument inserted into the method handle type,
1069 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1070 * The method and all its argument types must be accessible to the lookup object.
1071 * <p>
1072 * The returned method handle will have
1073 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1074 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1075 * <p>
1076 * If the returned method handle is invoked, the method's class will
1077 * be initialized, if it has not already been initialized.
1078 * <p><b>Example:</b>
1079 * <blockquote><pre>{@code
1080 import static java.lang.invoke.MethodHandles.*;
1081 import static java.lang.invoke.MethodType.*;
1082 ...
1083 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1084 "asList", methodType(List.class, Object[].class));
1085 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1086 * }</pre></blockquote>
1087 * @param refc the class from which the method is accessed
1088 * @param name the name of the method
1089 * @param type the type of the method
1090 * @return the desired method handle
1091 * @throws NoSuchMethodException if the method does not exist
1092 * @throws IllegalAccessException if access checking fails,
1093 * or if the method is not {@code static},
1094 * or if the method's variable arity modifier bit
1095 * is set and {@code asVarargsCollector} fails
1096 * @exception SecurityException if a security manager is present and it
1097 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1098 * @throws NullPointerException if any argument is null
1099 */
1100 public
1101 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1102 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1103 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1104 }
1105
1106 /**
1107 * Produces a method handle for a virtual method.
1108 * The type of the method handle will be that of the method,
1109 * with the receiver type (usually {@code refc}) prepended.
1110 * The method and all its argument types must be accessible to the lookup object.
1111 * <p>
1112 * When called, the handle will treat the first argument as a receiver
1113 * and, for non-private methods, dispatch on the receiver's type to determine which method
1114 * implementation to enter.
1115 * For private methods the named method in {@code refc} will be invoked on the receiver.
1116 * (The dispatching action is identical with that performed by an
1117 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1118 * <p>
1119 * The first argument will be of type {@code refc} if the lookup
1120 * class has full privileges to access the member. Otherwise
1121 * the member must be {@code protected} and the first argument
1122 * will be restricted in type to the lookup class.
1123 * <p>
1124 * The returned method handle will have
1125 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1126 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1127 * <p>
1128 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1129 * instructions and method handles produced by {@code findVirtual},
1130 * if the class is {@code MethodHandle} and the name string is
1131 * {@code invokeExact} or {@code invoke}, the resulting
1132 * method handle is equivalent to one produced by
1133 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1134 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1135 * with the same {@code type} argument.
1136 * <p>
1137 * If the class is {@code VarHandle} and the name string corresponds to
1138 * the name of a signature-polymorphic access mode method, the resulting
1139 * method handle is equivalent to one produced by
1140 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1141 * the access mode corresponding to the name string and with the same
1142 * {@code type} arguments.
1143 * <p>
1144 * <b>Example:</b>
1145 * <blockquote><pre>{@code
1146 import static java.lang.invoke.MethodHandles.*;
1147 import static java.lang.invoke.MethodType.*;
1148 ...
1149 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1150 "concat", methodType(String.class, String.class));
1151 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1152 "hashCode", methodType(int.class));
1153 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1154 "hashCode", methodType(int.class));
1155 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1156 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1157 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1158 // interface method:
1159 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1160 "subSequence", methodType(CharSequence.class, int.class, int.class));
1161 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1162 // constructor "internal method" must be accessed differently:
1163 MethodType MT_newString = methodType(void.class); //()V for new String()
1164 try { assertEquals("impossible", lookup()
1165 .findVirtual(String.class, "<init>", MT_newString));
1166 } catch (NoSuchMethodException ex) { } // OK
1167 MethodHandle MH_newString = publicLookup()
1168 .findConstructor(String.class, MT_newString);
1169 assertEquals("", (String) MH_newString.invokeExact());
1170 * }</pre></blockquote>
1171 *
1172 * @param refc the class or interface from which the method is accessed
1173 * @param name the name of the method
1174 * @param type the type of the method, with the receiver argument omitted
1175 * @return the desired method handle
1176 * @throws NoSuchMethodException if the method does not exist
1177 * @throws IllegalAccessException if access checking fails,
1178 * or if the method is {@code static},
1179 * or if the method's variable arity modifier bit
1180 * is set and {@code asVarargsCollector} fails
1181 * @exception SecurityException if a security manager is present and it
1182 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1183 * @throws NullPointerException if any argument is null
1184 */
1185 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1186 if (refc == MethodHandle.class) {
1187 MethodHandle mh = findVirtualForMH(name, type);
1188 if (mh != null) return mh;
1189 } else if (refc == VarHandle.class) {
1190 MethodHandle mh = findVirtualForVH(name, type);
1191 if (mh != null) return mh;
1192 }
1193 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1194 MemberName method = resolveOrFail(refKind, refc, name, type);
1195 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1196 }
1197 private MethodHandle findVirtualForMH(String name, MethodType type) {
1198 // these names require special lookups because of the implicit MethodType argument
1199 if ("invoke".equals(name))
1200 return invoker(type);
1201 if ("invokeExact".equals(name))
1202 return exactInvoker(type);
1203 assert(!MemberName.isMethodHandleInvokeName(name));
1204 return null;
1205 }
1206 private MethodHandle findVirtualForVH(String name, MethodType type) {
1207 try {
1208 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1209 } catch (IllegalArgumentException e) {
1210 return null;
1211 }
1212 }
1213
1214 /**
1215 * Produces a method handle which creates an object and initializes it, using
1216 * the constructor of the specified type.
1217 * The parameter types of the method handle will be those of the constructor,
1218 * while the return type will be a reference to the constructor's class.
1219 * The constructor and all its argument types must be accessible to the lookup object.
1220 * <p>
1221 * The requested type must have a return type of {@code void}.
1222 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1223 * <p>
1224 * The returned method handle will have
1225 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1226 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1227 * <p>
1228 * If the returned method handle is invoked, the constructor's class will
1229 * be initialized, if it has not already been initialized.
1230 * <p><b>Example:</b>
1231 * <blockquote><pre>{@code
1232 import static java.lang.invoke.MethodHandles.*;
1233 import static java.lang.invoke.MethodType.*;
1234 ...
1235 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1236 ArrayList.class, methodType(void.class, Collection.class));
1237 Collection orig = Arrays.asList("x", "y");
1238 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1239 assert(orig != copy);
1240 assertEquals(orig, copy);
1241 // a variable-arity constructor:
1242 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1243 ProcessBuilder.class, methodType(void.class, String[].class));
1244 ProcessBuilder pb = (ProcessBuilder)
1245 MH_newProcessBuilder.invoke("x", "y", "z");
1246 assertEquals("[x, y, z]", pb.command().toString());
1247 * }</pre></blockquote>
1248 * @param refc the class or interface from which the method is accessed
1249 * @param type the type of the method, with the receiver argument omitted, and a void return type
1250 * @return the desired method handle
1251 * @throws NoSuchMethodException if the constructor does not exist
1252 * @throws IllegalAccessException if access checking fails
1253 * or if the method's variable arity modifier bit
1254 * is set and {@code asVarargsCollector} fails
1255 * @exception SecurityException if a security manager is present and it
1256 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1257 * @throws NullPointerException if any argument is null
1258 */
1259 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1260 if (refc.isArray()) {
1261 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1262 }
1263 String name = "<init>";
1264 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1265 return getDirectConstructor(refc, ctor);
1266 }
1267
1268 /**
1269 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1270 * initializer of the class is not run.
1271 * <p>
1272 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1273 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1274 * load the requested class, and then determines whether the class is accessible to this lookup object.
1275 *
1276 * @param targetName the fully qualified name of the class to be looked up.
1277 * @return the requested class.
1278 * @exception SecurityException if a security manager is present and it
1279 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1280 * @throws LinkageError if the linkage fails
1281 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1282 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1283 * modes.
1284 * @exception SecurityException if a security manager is present and it
1285 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1286 * @since 9
1287 */
1288 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1289 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1290 return accessClass(targetClass);
1291 }
1292
1293 /**
1294 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1295 * static initializer of the class is not run.
1296 * <p>
1297 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1298 * {@linkplain #lookupModes() lookup modes}.
1299 *
1300 * @param targetClass the class to be access-checked
1301 *
1302 * @return the class that has been access-checked
1303 *
1304 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1305 * modes.
1306 * @exception SecurityException if a security manager is present and it
1307 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1308 * @since 9
1309 */
1310 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1311 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1312 throw new MemberName(targetClass).makeAccessException("access violation", this);
1313 }
1314 checkSecurityManager(targetClass, null);
1315 return targetClass;
1316 }
1317
1318 /**
1319 * Produces an early-bound method handle for a virtual method.
1320 * It will bypass checks for overriding methods on the receiver,
1321 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1322 * instruction from within the explicitly specified {@code specialCaller}.
1323 * The type of the method handle will be that of the method,
1324 * with a suitably restricted receiver type prepended.
1325 * (The receiver type will be {@code specialCaller} or a subtype.)
1326 * The method and all its argument types must be accessible
1327 * to the lookup object.
1328 * <p>
1329 * Before method resolution,
1330 * if the explicitly specified caller class is not identical with the
1331 * lookup class, or if this lookup object does not have
1332 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1333 * privileges, the access fails.
1334 * <p>
1335 * The returned method handle will have
1336 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1337 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1338 * <p style="font-size:smaller;">
1339 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1340 * even though the {@code invokespecial} instruction can refer to them
1341 * in special circumstances. Use {@link #findConstructor findConstructor}
1342 * to access instance initialization methods in a safe manner.)</em>
1343 * <p><b>Example:</b>
1344 * <blockquote><pre>{@code
1345 import static java.lang.invoke.MethodHandles.*;
1346 import static java.lang.invoke.MethodType.*;
1347 ...
1348 static class Listie extends ArrayList {
1349 public String toString() { return "[wee Listie]"; }
1350 static Lookup lookup() { return MethodHandles.lookup(); }
1351 }
1352 ...
1353 // no access to constructor via invokeSpecial:
1354 MethodHandle MH_newListie = Listie.lookup()
1355 .findConstructor(Listie.class, methodType(void.class));
1356 Listie l = (Listie) MH_newListie.invokeExact();
1357 try { assertEquals("impossible", Listie.lookup().findSpecial(
1358 Listie.class, "<init>", methodType(void.class), Listie.class));
1359 } catch (NoSuchMethodException ex) { } // OK
1360 // access to super and self methods via invokeSpecial:
1361 MethodHandle MH_super = Listie.lookup().findSpecial(
1362 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1363 MethodHandle MH_this = Listie.lookup().findSpecial(
1364 Listie.class, "toString" , methodType(String.class), Listie.class);
1365 MethodHandle MH_duper = Listie.lookup().findSpecial(
1366 Object.class, "toString" , methodType(String.class), Listie.class);
1367 assertEquals("[]", (String) MH_super.invokeExact(l));
1368 assertEquals(""+l, (String) MH_this.invokeExact(l));
1369 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1370 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1371 String.class, "toString", methodType(String.class), Listie.class));
1372 } catch (IllegalAccessException ex) { } // OK
1373 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1374 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1375 * }</pre></blockquote>
1376 *
1377 * @param refc the class or interface from which the method is accessed
1378 * @param name the name of the method (which must not be "<init>")
1379 * @param type the type of the method, with the receiver argument omitted
1380 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1381 * @return the desired method handle
1382 * @throws NoSuchMethodException if the method does not exist
1383 * @throws IllegalAccessException if access checking fails,
1384 * or if the method is {@code static},
1385 * or if the method's variable arity modifier bit
1386 * is set and {@code asVarargsCollector} fails
1387 * @exception SecurityException if a security manager is present and it
1388 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1389 * @throws NullPointerException if any argument is null
1390 */
1391 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1392 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1393 checkSpecialCaller(specialCaller, refc);
1394 Lookup specialLookup = this.in(specialCaller);
1395 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1396 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1397 }
1398
1399 /**
1400 * Produces a method handle giving read access to a non-static field.
1401 * The type of the method handle will have a return type of the field's
1402 * value type.
1403 * The method handle's single argument will be the instance containing
1404 * the field.
1405 * Access checking is performed immediately on behalf of the lookup class.
1406 * @param refc the class or interface from which the method is accessed
1407 * @param name the field's name
1408 * @param type the field's type
1409 * @return a method handle which can load values from the field
1410 * @throws NoSuchFieldException if the field does not exist
1411 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1412 * @exception SecurityException if a security manager is present and it
1413 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1414 * @throws NullPointerException if any argument is null
1415 * @see #findVarHandle(Class, String, Class)
1416 */
1417 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1418 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1419 return getDirectField(REF_getField, refc, field);
1420 }
1421
1422 /**
1423 * Produces a method handle giving write access to a non-static field.
1424 * The type of the method handle will have a void return type.
1425 * The method handle will take two arguments, the instance containing
1426 * the field, and the value to be stored.
1427 * The second argument will be of the field's value type.
1428 * Access checking is performed immediately on behalf of the lookup class.
1429 * @param refc the class or interface from which the method is accessed
1430 * @param name the field's name
1431 * @param type the field's type
1432 * @return a method handle which can store values into the field
1433 * @throws NoSuchFieldException if the field does not exist
1434 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1435 * @exception SecurityException if a security manager is present and it
1436 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1437 * @throws NullPointerException if any argument is null
1438 * @see #findVarHandle(Class, String, Class)
1439 */
1440 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1441 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1442 return getDirectField(REF_putField, refc, field);
1443 }
1444
1445 /**
1446 * Produces a VarHandle giving access to a non-static field {@code name}
1447 * of type {@code type} declared in a class of type {@code recv}.
1448 * The VarHandle's variable type is {@code type} and it has one
1449 * coordinate type, {@code recv}.
1450 * <p>
1451 * Access checking is performed immediately on behalf of the lookup
1452 * class.
1453 * <p>
1454 * Certain access modes of the returned VarHandle are unsupported under
1455 * the following conditions:
1456 * <ul>
1457 * <li>if the field is declared {@code final}, then the write, atomic
1458 * update, numeric atomic update, and bitwise atomic update access
1459 * modes are unsupported.
1460 * <li>if the field type is anything other than {@code byte},
1461 * {@code short}, {@code char}, {@code int}, {@code long},
1462 * {@code float}, or {@code double} then numeric atomic update
1463 * access modes are unsupported.
1464 * <li>if the field type is anything other than {@code boolean},
1465 * {@code byte}, {@code short}, {@code char}, {@code int} or
1466 * {@code long} then bitwise atomic update access modes are
1467 * unsupported.
1468 * </ul>
1469 * <p>
1470 * If the field is declared {@code volatile} then the returned VarHandle
1471 * will override access to the field (effectively ignore the
1472 * {@code volatile} declaration) in accordance to its specified
1473 * access modes.
1474 * <p>
1475 * If the field type is {@code float} or {@code double} then numeric
1476 * and atomic update access modes compare values using their bitwise
1477 * representation (see {@link Float#floatToRawIntBits} and
1478 * {@link Double#doubleToRawLongBits}, respectively).
1479 * @apiNote
1480 * Bitwise comparison of {@code float} values or {@code double} values,
1481 * as performed by the numeric and atomic update access modes, differ
1482 * from the primitive {@code ==} operator and the {@link Float#equals}
1483 * and {@link Double#equals} methods, specifically with respect to
1484 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1485 * Care should be taken when performing a compare and set or a compare
1486 * and exchange operation with such values since the operation may
1487 * unexpectedly fail.
1488 * There are many possible NaN values that are considered to be
1489 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1490 * provided by Java can distinguish between them. Operation failure can
1491 * occur if the expected or witness value is a NaN value and it is
1492 * transformed (perhaps in a platform specific manner) into another NaN
1493 * value, and thus has a different bitwise representation (see
1494 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1495 * details).
1496 * The values {@code -0.0} and {@code +0.0} have different bitwise
1497 * representations but are considered equal when using the primitive
1498 * {@code ==} operator. Operation failure can occur if, for example, a
1499 * numeric algorithm computes an expected value to be say {@code -0.0}
1500 * and previously computed the witness value to be say {@code +0.0}.
1501 * @param recv the receiver class, of type {@code R}, that declares the
1502 * non-static field
1503 * @param name the field's name
1504 * @param type the field's type, of type {@code T}
1505 * @return a VarHandle giving access to non-static fields.
1506 * @throws NoSuchFieldException if the field does not exist
1507 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1508 * @exception SecurityException if a security manager is present and it
1509 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1510 * @throws NullPointerException if any argument is null
1511 * @since 9
1512 */
1513 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1514 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1515 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1516 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1517 }
1518
1519 /**
1520 * Produces a method handle giving read access to a static field.
1521 * The type of the method handle will have a return type of the field's
1522 * value type.
1523 * The method handle will take no arguments.
1524 * Access checking is performed immediately on behalf of the lookup class.
1525 * <p>
1526 * If the returned method handle is invoked, the field's class will
1527 * be initialized, if it has not already been initialized.
1528 * @param refc the class or interface from which the method is accessed
1529 * @param name the field's name
1530 * @param type the field's type
1531 * @return a method handle which can load values from the field
1532 * @throws NoSuchFieldException if the field does not exist
1533 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1534 * @exception SecurityException if a security manager is present and it
1535 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1536 * @throws NullPointerException if any argument is null
1537 */
1538 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1539 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1540 return getDirectField(REF_getStatic, refc, field);
1541 }
1542
1543 /**
1544 * Produces a method handle giving write access to a static field.
1545 * The type of the method handle will have a void return type.
1546 * The method handle will take a single
1547 * argument, of the field's value type, the value to be stored.
1548 * Access checking is performed immediately on behalf of the lookup class.
1549 * <p>
1550 * If the returned method handle is invoked, the field's class will
1551 * be initialized, if it has not already been initialized.
1552 * @param refc the class or interface from which the method is accessed
1553 * @param name the field's name
1554 * @param type the field's type
1555 * @return a method handle which can store values into the field
1556 * @throws NoSuchFieldException if the field does not exist
1557 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1558 * @exception SecurityException if a security manager is present and it
1559 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1560 * @throws NullPointerException if any argument is null
1561 */
1562 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1563 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1564 return getDirectField(REF_putStatic, refc, field);
1565 }
1566
1567 /**
1568 * Produces a VarHandle giving access to a static field {@code name} of
1569 * type {@code type} declared in a class of type {@code decl}.
1570 * The VarHandle's variable type is {@code type} and it has no
1571 * coordinate types.
1572 * <p>
1573 * Access checking is performed immediately on behalf of the lookup
1574 * class.
1575 * <p>
1576 * If the returned VarHandle is operated on, the declaring class will be
1577 * initialized, if it has not already been initialized.
1578 * <p>
1579 * Certain access modes of the returned VarHandle are unsupported under
1580 * the following conditions:
1581 * <ul>
1582 * <li>if the field is declared {@code final}, then the write, atomic
1583 * update, numeric atomic update, and bitwise atomic update access
1584 * modes are unsupported.
1585 * <li>if the field type is anything other than {@code byte},
1586 * {@code short}, {@code char}, {@code int}, {@code long},
1587 * {@code float}, or {@code double}, then numeric atomic update
1588 * access modes are unsupported.
1589 * <li>if the field type is anything other than {@code boolean},
1590 * {@code byte}, {@code short}, {@code char}, {@code int} or
1591 * {@code long} then bitwise atomic update access modes are
1592 * unsupported.
1593 * </ul>
1594 * <p>
1595 * If the field is declared {@code volatile} then the returned VarHandle
1596 * will override access to the field (effectively ignore the
1597 * {@code volatile} declaration) in accordance to its specified
1598 * access modes.
1599 * <p>
1600 * If the field type is {@code float} or {@code double} then numeric
1601 * and atomic update access modes compare values using their bitwise
1602 * representation (see {@link Float#floatToRawIntBits} and
1603 * {@link Double#doubleToRawLongBits}, respectively).
1604 * @apiNote
1605 * Bitwise comparison of {@code float} values or {@code double} values,
1606 * as performed by the numeric and atomic update access modes, differ
1607 * from the primitive {@code ==} operator and the {@link Float#equals}
1608 * and {@link Double#equals} methods, specifically with respect to
1609 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1610 * Care should be taken when performing a compare and set or a compare
1611 * and exchange operation with such values since the operation may
1612 * unexpectedly fail.
1613 * There are many possible NaN values that are considered to be
1614 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1615 * provided by Java can distinguish between them. Operation failure can
1616 * occur if the expected or witness value is a NaN value and it is
1617 * transformed (perhaps in a platform specific manner) into another NaN
1618 * value, and thus has a different bitwise representation (see
1619 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1620 * details).
1621 * The values {@code -0.0} and {@code +0.0} have different bitwise
1622 * representations but are considered equal when using the primitive
1623 * {@code ==} operator. Operation failure can occur if, for example, a
1624 * numeric algorithm computes an expected value to be say {@code -0.0}
1625 * and previously computed the witness value to be say {@code +0.0}.
1626 * @param decl the class that declares the static field
1627 * @param name the field's name
1628 * @param type the field's type, of type {@code T}
1629 * @return a VarHandle giving access to a static field
1630 * @throws NoSuchFieldException if the field does not exist
1631 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1632 * @exception SecurityException if a security manager is present and it
1633 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1634 * @throws NullPointerException if any argument is null
1635 * @since 9
1636 */
1637 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1638 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1639 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1640 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1641 }
1642
1643 /**
1644 * Produces an early-bound method handle for a non-static method.
1645 * The receiver must have a supertype {@code defc} in which a method
1646 * of the given name and type is accessible to the lookup class.
1647 * The method and all its argument types must be accessible to the lookup object.
1648 * The type of the method handle will be that of the method,
1649 * without any insertion of an additional receiver parameter.
1650 * The given receiver will be bound into the method handle,
1651 * so that every call to the method handle will invoke the
1652 * requested method on the given receiver.
1653 * <p>
1654 * The returned method handle will have
1655 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1656 * the method's variable arity modifier bit ({@code 0x0080}) is set
1657 * <em>and</em> the trailing array argument is not the only argument.
1658 * (If the trailing array argument is the only argument,
1659 * the given receiver value will be bound to it.)
1660 * <p>
1661 * This is almost equivalent to the following code, with some differences noted below:
1662 * <blockquote><pre>{@code
1663 import static java.lang.invoke.MethodHandles.*;
1664 import static java.lang.invoke.MethodType.*;
1665 ...
1666 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1667 MethodHandle mh1 = mh0.bindTo(receiver);
1668 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1669 return mh1;
1670 * }</pre></blockquote>
1671 * where {@code defc} is either {@code receiver.getClass()} or a super
1672 * type of that class, in which the requested method is accessible
1673 * to the lookup class.
1674 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
1675 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
1676 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
1677 * the receiver is restricted by {@code findVirtual} to the lookup class.)
1678 * @param receiver the object from which the method is accessed
1679 * @param name the name of the method
1680 * @param type the type of the method, with the receiver argument omitted
1681 * @return the desired method handle
1682 * @throws NoSuchMethodException if the method does not exist
1683 * @throws IllegalAccessException if access checking fails
1684 * or if the method's variable arity modifier bit
1685 * is set and {@code asVarargsCollector} fails
1686 * @exception SecurityException if a security manager is present and it
1687 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1688 * @throws NullPointerException if any argument is null
1689 * @see MethodHandle#bindTo
1690 * @see #findVirtual
1691 */
1692 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1693 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1694 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1695 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
1696 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
1697 throw new IllegalAccessException("The restricted defining class " +
1698 mh.type().leadingReferenceParameter().getName() +
1699 " is not assignable from receiver class " +
1700 receiver.getClass().getName());
1701 }
1702 return mh.bindArgumentL(0, receiver).setVarargs(method);
1703 }
1704
1705 /**
1706 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1707 * to <i>m</i>, if the lookup class has permission.
1708 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1709 * If <i>m</i> is virtual, overriding is respected on every call.
1710 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1711 * The type of the method handle will be that of the method,
1712 * with the receiver type prepended (but only if it is non-static).
1713 * If the method's {@code accessible} flag is not set,
1714 * access checking is performed immediately on behalf of the lookup class.
1715 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1716 * <p>
1717 * The returned method handle will have
1718 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1719 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1720 * <p>
1721 * If <i>m</i> is static, and
1722 * if the returned method handle is invoked, the method's class will
1723 * be initialized, if it has not already been initialized.
1724 * @param m the reflected method
1725 * @return a method handle which can invoke the reflected method
1726 * @throws IllegalAccessException if access checking fails
1727 * or if the method's variable arity modifier bit
1728 * is set and {@code asVarargsCollector} fails
1729 * @throws NullPointerException if the argument is null
1730 */
1731 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1732 if (m.getDeclaringClass() == MethodHandle.class) {
1733 MethodHandle mh = unreflectForMH(m);
1734 if (mh != null) return mh;
1735 }
1736 if (m.getDeclaringClass() == VarHandle.class) {
1737 MethodHandle mh = unreflectForVH(m);
1738 if (mh != null) return mh;
1739 }
1740 MemberName method = new MemberName(m);
1741 byte refKind = method.getReferenceKind();
1742 if (refKind == REF_invokeSpecial)
1743 refKind = REF_invokeVirtual;
1744 assert(method.isMethod());
1745 @SuppressWarnings("deprecation")
1746 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1747 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1748 }
1749 private MethodHandle unreflectForMH(Method m) {
1750 // these names require special lookups because they throw UnsupportedOperationException
1751 if (MemberName.isMethodHandleInvokeName(m.getName()))
1752 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1753 return null;
1754 }
1755 private MethodHandle unreflectForVH(Method m) {
1756 // these names require special lookups because they throw UnsupportedOperationException
1757 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1758 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1759 return null;
1760 }
1761
1762 /**
1763 * Produces a method handle for a reflected method.
1764 * It will bypass checks for overriding methods on the receiver,
1765 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1766 * instruction from within the explicitly specified {@code specialCaller}.
1767 * The type of the method handle will be that of the method,
1768 * with a suitably restricted receiver type prepended.
1769 * (The receiver type will be {@code specialCaller} or a subtype.)
1770 * If the method's {@code accessible} flag is not set,
1771 * access checking is performed immediately on behalf of the lookup class,
1772 * as if {@code invokespecial} instruction were being linked.
1773 * <p>
1774 * Before method resolution,
1775 * if the explicitly specified caller class is not identical with the
1776 * lookup class, or if this lookup object does not have
1777 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1778 * privileges, the access fails.
1779 * <p>
1780 * The returned method handle will have
1781 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1782 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1783 * @param m the reflected method
1784 * @param specialCaller the class nominally calling the method
1785 * @return a method handle which can invoke the reflected method
1786 * @throws IllegalAccessException if access checking fails,
1787 * or if the method is {@code static},
1788 * or if the method's variable arity modifier bit
1789 * is set and {@code asVarargsCollector} fails
1790 * @throws NullPointerException if any argument is null
1791 */
1792 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1793 checkSpecialCaller(specialCaller, null);
1794 Lookup specialLookup = this.in(specialCaller);
1795 MemberName method = new MemberName(m, true);
1796 assert(method.isMethod());
1797 // ignore m.isAccessible: this is a new kind of access
1798 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1799 }
1800
1801 /**
1802 * Produces a method handle for a reflected constructor.
1803 * The type of the method handle will be that of the constructor,
1804 * with the return type changed to the declaring class.
1805 * The method handle will perform a {@code newInstance} operation,
1806 * creating a new instance of the constructor's class on the
1807 * arguments passed to the method handle.
1808 * <p>
1809 * If the constructor's {@code accessible} flag is not set,
1810 * access checking is performed immediately on behalf of the lookup class.
1811 * <p>
1812 * The returned method handle will have
1813 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1814 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1815 * <p>
1816 * If the returned method handle is invoked, the constructor's class will
1817 * be initialized, if it has not already been initialized.
1818 * @param c the reflected constructor
1819 * @return a method handle which can invoke the reflected constructor
1820 * @throws IllegalAccessException if access checking fails
1821 * or if the method's variable arity modifier bit
1822 * is set and {@code asVarargsCollector} fails
1823 * @throws NullPointerException if the argument is null
1824 */
1825 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1826 MemberName ctor = new MemberName(c);
1827 assert(ctor.isConstructor());
1828 @SuppressWarnings("deprecation")
1829 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1830 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1831 }
1832
1833 /**
1834 * Produces a method handle giving read access to a reflected field.
1835 * The type of the method handle will have a return type of the field's
1836 * value type.
1837 * If the field is static, the method handle will take no arguments.
1838 * Otherwise, its single argument will be the instance containing
1839 * the field.
1840 * If the field's {@code accessible} flag is not set,
1841 * access checking is performed immediately on behalf of the lookup class.
1842 * <p>
1843 * If the field is static, and
1844 * if the returned method handle is invoked, the field's class will
1845 * be initialized, if it has not already been initialized.
1846 * @param f the reflected field
1847 * @return a method handle which can load values from the reflected field
1848 * @throws IllegalAccessException if access checking fails
1849 * @throws NullPointerException if the argument is null
1850 */
1851 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1852 return unreflectField(f, false);
1853 }
1854 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1855 MemberName field = new MemberName(f, isSetter);
1856 assert(isSetter
1857 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1858 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1859 @SuppressWarnings("deprecation")
1860 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1861 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1862 }
1863
1864 /**
1865 * Produces a method handle giving write access to a reflected field.
1866 * The type of the method handle will have a void return type.
1867 * If the field is static, the method handle will take a single
1868 * argument, of the field's value type, the value to be stored.
1869 * Otherwise, the two arguments will be the instance containing
1870 * the field, and the value to be stored.
1871 * If the field's {@code accessible} flag is not set,
1872 * access checking is performed immediately on behalf of the lookup class.
1873 * <p>
1874 * If the field is static, and
1875 * if the returned method handle is invoked, the field's class will
1876 * be initialized, if it has not already been initialized.
1877 * @param f the reflected field
1878 * @return a method handle which can store values into the reflected field
1879 * @throws IllegalAccessException if access checking fails
1880 * @throws NullPointerException if the argument is null
1881 */
1882 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1883 return unreflectField(f, true);
1884 }
1885
1886 /**
1887 * Produces a VarHandle giving access to a reflected field {@code f}
1888 * of type {@code T} declared in a class of type {@code R}.
1889 * The VarHandle's variable type is {@code T}.
1890 * If the field is non-static the VarHandle has one coordinate type,
1891 * {@code R}. Otherwise, the field is static, and the VarHandle has no
1892 * coordinate types.
1893 * <p>
1894 * Access checking is performed immediately on behalf of the lookup
1895 * class, regardless of the value of the field's {@code accessible}
1896 * flag.
1897 * <p>
1898 * If the field is static, and if the returned VarHandle is operated
1899 * on, the field's declaring class will be initialized, if it has not
1900 * already been initialized.
1901 * <p>
1902 * Certain access modes of the returned VarHandle are unsupported under
1903 * the following conditions:
1904 * <ul>
1905 * <li>if the field is declared {@code final}, then the write, atomic
1906 * update, numeric atomic update, and bitwise atomic update access
1907 * modes are unsupported.
1908 * <li>if the field type is anything other than {@code byte},
1909 * {@code short}, {@code char}, {@code int}, {@code long},
1910 * {@code float}, or {@code double} then numeric atomic update
1911 * access modes are unsupported.
1912 * <li>if the field type is anything other than {@code boolean},
1913 * {@code byte}, {@code short}, {@code char}, {@code int} or
1914 * {@code long} then bitwise atomic update access modes are
1915 * unsupported.
1916 * </ul>
1917 * <p>
1918 * If the field is declared {@code volatile} then the returned VarHandle
1919 * will override access to the field (effectively ignore the
1920 * {@code volatile} declaration) in accordance to its specified
1921 * access modes.
1922 * <p>
1923 * If the field type is {@code float} or {@code double} then numeric
1924 * and atomic update access modes compare values using their bitwise
1925 * representation (see {@link Float#floatToRawIntBits} and
1926 * {@link Double#doubleToRawLongBits}, respectively).
1927 * @apiNote
1928 * Bitwise comparison of {@code float} values or {@code double} values,
1929 * as performed by the numeric and atomic update access modes, differ
1930 * from the primitive {@code ==} operator and the {@link Float#equals}
1931 * and {@link Double#equals} methods, specifically with respect to
1932 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1933 * Care should be taken when performing a compare and set or a compare
1934 * and exchange operation with such values since the operation may
1935 * unexpectedly fail.
1936 * There are many possible NaN values that are considered to be
1937 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1938 * provided by Java can distinguish between them. Operation failure can
1939 * occur if the expected or witness value is a NaN value and it is
1940 * transformed (perhaps in a platform specific manner) into another NaN
1941 * value, and thus has a different bitwise representation (see
1942 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1943 * details).
1944 * The values {@code -0.0} and {@code +0.0} have different bitwise
1945 * representations but are considered equal when using the primitive
1946 * {@code ==} operator. Operation failure can occur if, for example, a
1947 * numeric algorithm computes an expected value to be say {@code -0.0}
1948 * and previously computed the witness value to be say {@code +0.0}.
1949 * @param f the reflected field, with a field of type {@code T}, and
1950 * a declaring class of type {@code R}
1951 * @return a VarHandle giving access to non-static fields or a static
1952 * field
1953 * @throws IllegalAccessException if access checking fails
1954 * @throws NullPointerException if the argument is null
1955 * @since 9
1956 */
1957 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1958 MemberName getField = new MemberName(f, false);
1959 MemberName putField = new MemberName(f, true);
1960 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1961 f.getDeclaringClass(), getField, putField);
1962 }
1963
1964 /**
1965 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1966 * created by this lookup object or a similar one.
1967 * Security and access checks are performed to ensure that this lookup object
1968 * is capable of reproducing the target method handle.
1969 * This means that the cracking may fail if target is a direct method handle
1970 * but was created by an unrelated lookup object.
1971 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1972 * and was created by a lookup object for a different class.
1973 * @param target a direct method handle to crack into symbolic reference components
1974 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1975 * @exception SecurityException if a security manager is present and it
1976 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1977 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1978 * @exception NullPointerException if the target is {@code null}
1979 * @see MethodHandleInfo
1980 * @since 1.8
1981 */
1982 public MethodHandleInfo revealDirect(MethodHandle target) {
1983 MemberName member = target.internalMemberName();
1984 if (member == null || (!member.isResolved() &&
1985 !member.isMethodHandleInvoke() &&
1986 !member.isVarHandleMethodInvoke()))
1987 throw newIllegalArgumentException("not a direct method handle");
1988 Class<?> defc = member.getDeclaringClass();
1989 byte refKind = member.getReferenceKind();
1990 assert(MethodHandleNatives.refKindIsValid(refKind));
1991 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1992 // Devirtualized method invocation is usually formally virtual.
1993 // To avoid creating extra MemberName objects for this common case,
1994 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1995 refKind = REF_invokeVirtual;
1996 if (refKind == REF_invokeVirtual && defc.isInterface())
1997 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1998 refKind = REF_invokeInterface;
1999 // Check SM permissions and member access before cracking.
2000 try {
2001 checkAccess(refKind, defc, member);
2002 checkSecurityManager(defc, member);
2003 } catch (IllegalAccessException ex) {
2004 throw new IllegalArgumentException(ex);
2005 }
2006 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2007 Class<?> callerClass = target.internalCallerClass();
2008 if (!hasPrivateAccess() || callerClass != lookupClass())
2009 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2010 }
2011 // Produce the handle to the results.
2012 return new InfoFromMemberName(this, member, refKind);
2013 }
2014
2015 /// Helper methods, all package-private.
2016
2017 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2018 checkSymbolicClass(refc); // do this before attempting to resolve
2019 Objects.requireNonNull(name);
2020 Objects.requireNonNull(type);
2021 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2022 NoSuchFieldException.class);
2023 }
2024
2025 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2026 checkSymbolicClass(refc); // do this before attempting to resolve
2027 Objects.requireNonNull(name);
2028 Objects.requireNonNull(type);
2029 checkMethodName(refKind, name); // NPE check on name
2030 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2031 NoSuchMethodException.class);
2032 }
2033
2034 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2035 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2036 Objects.requireNonNull(member.getName());
2037 Objects.requireNonNull(member.getType());
2038 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2039 ReflectiveOperationException.class);
2040 }
2041
2042 MemberName resolveOrNull(byte refKind, MemberName member) {
2043 // do this before attempting to resolve
2044 if (!isClassAccessible(member.getDeclaringClass())) {
2045 return null;
2046 }
2047 Objects.requireNonNull(member.getName());
2048 Objects.requireNonNull(member.getType());
2049 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
2050 }
2051
2052 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2053 if (!isClassAccessible(refc)) {
2054 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2055 }
2056 }
2057
2058 boolean isClassAccessible(Class<?> refc) {
2059 Objects.requireNonNull(refc);
2060 Class<?> caller = lookupClassOrNull();
2061 return caller == null || VerifyAccess.isClassAccessible(refc, caller, allowedModes);
2062 }
2063
2064 /** Check name for an illegal leading "<" character. */
2065 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2066 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2067 throw new NoSuchMethodException("illegal method name: "+name);
2068 }
2069
2070
2071 /**
2072 * Find my trustable caller class if m is a caller sensitive method.
2073 * If this lookup object has private access, then the caller class is the lookupClass.
2074 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2075 */
2076 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2077 Class<?> callerClass = null;
2078 if (MethodHandleNatives.isCallerSensitive(m)) {
2079 // Only lookups with private access are allowed to resolve caller-sensitive methods
2080 if (hasPrivateAccess()) {
2081 callerClass = lookupClass;
2082 } else {
2083 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2084 }
2085 }
2086 return callerClass;
2087 }
2088
2089 /**
2090 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2091 * @return {@code true} if this lookup has {@code PRIVATE} access.
2092 * @since 9
2093 */
2094 public boolean hasPrivateAccess() {
2095 return (allowedModes & PRIVATE) != 0;
2096 }
2097
2098 /**
2099 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2100 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2101 * If this lookup object has private access, then the caller class is the lookupClass.
2102 */
2103 void checkSecurityManager(Class<?> refc, MemberName m) {
2104 SecurityManager smgr = System.getSecurityManager();
2105 if (smgr == null) return;
2106 if (allowedModes == TRUSTED) return;
2107
2108 // Step 1:
2109 boolean fullPowerLookup = hasPrivateAccess();
2110 if (!fullPowerLookup ||
2111 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2112 ReflectUtil.checkPackageAccess(refc);
2113 }
2114
2115 if (m == null) { // findClass or accessClass
2116 // Step 2b:
2117 if (!fullPowerLookup) {
2118 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2119 }
2120 return;
2121 }
2122
2123 // Step 2a:
2124 if (m.isPublic()) return;
2125 if (!fullPowerLookup) {
2126 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2127 }
2128
2129 // Step 3:
2130 Class<?> defc = m.getDeclaringClass();
2131 if (!fullPowerLookup && defc != refc) {
2132 ReflectUtil.checkPackageAccess(defc);
2133 }
2134 }
2135
2136 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2137 boolean wantStatic = (refKind == REF_invokeStatic);
2138 String message;
2139 if (m.isConstructor())
2140 message = "expected a method, not a constructor";
2141 else if (!m.isMethod())
2142 message = "expected a method";
2143 else if (wantStatic != m.isStatic())
2144 message = wantStatic ? "expected a static method" : "expected a non-static method";
2145 else
2146 { checkAccess(refKind, refc, m); return; }
2147 throw m.makeAccessException(message, this);
2148 }
2149
2150 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2151 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2152 String message;
2153 if (wantStatic != m.isStatic())
2154 message = wantStatic ? "expected a static field" : "expected a non-static field";
2155 else
2156 { checkAccess(refKind, refc, m); return; }
2157 throw m.makeAccessException(message, this);
2158 }
2159
2160 /** Check public/protected/private bits on the symbolic reference class and its member. */
2161 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2162 assert(m.referenceKindIsConsistentWith(refKind) &&
2163 MethodHandleNatives.refKindIsValid(refKind) &&
2164 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2165 int allowedModes = this.allowedModes;
2166 if (allowedModes == TRUSTED) return;
2167 int mods = m.getModifiers();
2168 if (Modifier.isProtected(mods) &&
2169 refKind == REF_invokeVirtual &&
2170 m.getDeclaringClass() == Object.class &&
2171 m.getName().equals("clone") &&
2172 refc.isArray()) {
2173 // The JVM does this hack also.
2174 // (See ClassVerifier::verify_invoke_instructions
2175 // and LinkResolver::check_method_accessability.)
2176 // Because the JVM does not allow separate methods on array types,
2177 // there is no separate method for int[].clone.
2178 // All arrays simply inherit Object.clone.
2179 // But for access checking logic, we make Object.clone
2180 // (normally protected) appear to be public.
2181 // Later on, when the DirectMethodHandle is created,
2182 // its leading argument will be restricted to the
2183 // requested array type.
2184 // N.B. The return type is not adjusted, because
2185 // that is *not* the bytecode behavior.
2186 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2187 }
2188 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2189 // cannot "new" a protected ctor in a different package
2190 mods ^= Modifier.PROTECTED;
2191 }
2192 if (Modifier.isFinal(mods) &&
2193 MethodHandleNatives.refKindIsSetter(refKind))
2194 throw m.makeAccessException("unexpected set of a final field", this);
2195 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2196 if ((requestedModes & allowedModes) != 0) {
2197 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2198 mods, lookupClass(), allowedModes))
2199 return;
2200 } else {
2201 // Protected members can also be checked as if they were package-private.
2202 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2203 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2204 return;
2205 }
2206 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2207 }
2208
2209 String accessFailedMessage(Class<?> refc, MemberName m) {
2210 Class<?> defc = m.getDeclaringClass();
2211 int mods = m.getModifiers();
2212 // check the class first:
2213 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2214 (defc == refc ||
2215 Modifier.isPublic(refc.getModifiers())));
2216 if (!classOK && (allowedModes & PACKAGE) != 0) {
2217 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2218 (defc == refc ||
2219 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2220 }
2221 if (!classOK)
2222 return "class is not public";
2223 if (Modifier.isPublic(mods))
2224 return "access to public member failed"; // (how?, module not readable?)
2225 if (Modifier.isPrivate(mods))
2226 return "member is private";
2227 if (Modifier.isProtected(mods))
2228 return "member is protected";
2229 return "member is private to package";
2230 }
2231
2232 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2233 int allowedModes = this.allowedModes;
2234 if (allowedModes == TRUSTED) return;
2235 if (!hasPrivateAccess()
2236 || (specialCaller != lookupClass()
2237 // ensure non-abstract methods in superinterfaces can be special-invoked
2238 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
2239 throw new MemberName(specialCaller).
2240 makeAccessException("no private access for invokespecial", this);
2241 }
2242
2243 private boolean restrictProtectedReceiver(MemberName method) {
2244 // The accessing class only has the right to use a protected member
2245 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2246 if (!method.isProtected() || method.isStatic()
2247 || allowedModes == TRUSTED
2248 || method.getDeclaringClass() == lookupClass()
2249 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
2250 return false;
2251 return true;
2252 }
2253 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2254 assert(!method.isStatic());
2255 // receiver type of mh is too wide; narrow to caller
2256 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2257 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2258 }
2259 MethodType rawType = mh.type();
2260 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2261 MethodType narrowType = rawType.changeParameterType(0, caller);
2262 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2263 assert(mh.viewAsTypeChecks(narrowType, true));
2264 return mh.copyWith(narrowType, mh.form);
2265 }
2266
2267 /** Check access and get the requested method. */
2268 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2269 final boolean doRestrict = true;
2270 final boolean checkSecurity = true;
2271 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2272 }
2273 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2274 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2275 final boolean doRestrict = false;
2276 final boolean checkSecurity = true;
2277 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, boundCallerClass);
2278 }
2279 /** Check access and get the requested method, eliding security manager checks. */
2280 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2281 final boolean doRestrict = true;
2282 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2283 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2284 }
2285 /** Common code for all methods; do not call directly except from immediately above. */
2286 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2287 boolean checkSecurity,
2288 boolean doRestrict, Class<?> boundCallerClass) throws IllegalAccessException {
2289
2290 checkMethod(refKind, refc, method);
2291 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2292 if (checkSecurity)
2293 checkSecurityManager(refc, method);
2294 assert(!method.isMethodHandleInvoke());
2295
2296 if (refKind == REF_invokeSpecial &&
2297 refc != lookupClass() &&
2298 !refc.isInterface() &&
2299 refc != lookupClass().getSuperclass() &&
2300 refc.isAssignableFrom(lookupClass())) {
2301 assert(!method.getName().equals("<init>")); // not this code path
2302
2303 // Per JVMS 6.5, desc. of invokespecial instruction:
2304 // If the method is in a superclass of the LC,
2305 // and if our original search was above LC.super,
2306 // repeat the search (symbolic lookup) from LC.super
2307 // and continue with the direct superclass of that class,
2308 // and so forth, until a match is found or no further superclasses exist.
2309 // FIXME: MemberName.resolve should handle this instead.
2310 Class<?> refcAsSuper = lookupClass();
2311 MemberName m2;
2312 do {
2313 refcAsSuper = refcAsSuper.getSuperclass();
2314 m2 = new MemberName(refcAsSuper,
2315 method.getName(),
2316 method.getMethodType(),
2317 REF_invokeSpecial);
2318 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2319 } while (m2 == null && // no method is found yet
2320 refc != refcAsSuper); // search up to refc
2321 if (m2 == null) throw new InternalError(method.toString());
2322 method = m2;
2323 refc = refcAsSuper;
2324 // redo basic checks
2325 checkMethod(refKind, refc, method);
2326 }
2327
2328 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
2329 MethodHandle mh = dmh;
2330 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
2331 if ((doRestrict && refKind == REF_invokeSpecial) ||
2332 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2333 mh = restrictReceiver(method, dmh, lookupClass());
2334 }
2335 mh = maybeBindCaller(method, mh, boundCallerClass);
2336 mh = mh.setVarargs(method);
2337 return mh;
2338 }
2339 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2340 Class<?> boundCallerClass)
2341 throws IllegalAccessException {
2342 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2343 return mh;
2344 Class<?> hostClass = lookupClass;
2345 if (!hasPrivateAccess()) // caller must have private access
2346 hostClass = boundCallerClass; // boundCallerClass came from a security manager style stack walk
2347 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2348 // Note: caller will apply varargs after this step happens.
2349 return cbmh;
2350 }
2351 /** Check access and get the requested field. */
2352 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2353 final boolean checkSecurity = true;
2354 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2355 }
2356 /** Check access and get the requested field, eliding security manager checks. */
2357 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2358 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2359 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2360 }
2361 /** Common code for all fields; do not call directly except from immediately above. */
2362 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2363 boolean checkSecurity) throws IllegalAccessException {
2364 checkField(refKind, refc, field);
2365 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2366 if (checkSecurity)
2367 checkSecurityManager(refc, field);
2368 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2369 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2370 restrictProtectedReceiver(field));
2371 if (doRestrict)
2372 return restrictReceiver(field, dmh, lookupClass());
2373 return dmh;
2374 }
2375 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2376 Class<?> refc, MemberName getField, MemberName putField)
2377 throws IllegalAccessException {
2378 final boolean checkSecurity = true;
2379 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2380 }
2381 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2382 Class<?> refc, MemberName getField, MemberName putField)
2383 throws IllegalAccessException {
2384 final boolean checkSecurity = false;
2385 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2386 }
2387 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2388 Class<?> refc, MemberName getField, MemberName putField,
2389 boolean checkSecurity) throws IllegalAccessException {
2390 assert getField.isStatic() == putField.isStatic();
2391 assert getField.isGetter() && putField.isSetter();
2392 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2393 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2394
2395 checkField(getRefKind, refc, getField);
2396 if (checkSecurity)
2397 checkSecurityManager(refc, getField);
2398
2399 if (!putField.isFinal()) {
2400 // A VarHandle does not support updates to final fields, any
2401 // such VarHandle to a final field will be read-only and
2402 // therefore the following write-based accessibility checks are
2403 // only required for non-final fields
2404 checkField(putRefKind, refc, putField);
2405 if (checkSecurity)
2406 checkSecurityManager(refc, putField);
2407 }
2408
2409 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2410 restrictProtectedReceiver(getField));
2411 if (doRestrict) {
2412 assert !getField.isStatic();
2413 // receiver type of VarHandle is too wide; narrow to caller
2414 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2415 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2416 }
2417 refc = lookupClass();
2418 }
2419 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2420 }
2421 /** Check access and get the requested constructor. */
2422 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2423 final boolean checkSecurity = true;
2424 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2425 }
2426 /** Check access and get the requested constructor, eliding security manager checks. */
2427 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2428 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2429 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2430 }
2431 /** Common code for all constructors; do not call directly except from immediately above. */
2432 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2433 boolean checkSecurity) throws IllegalAccessException {
2434 assert(ctor.isConstructor());
2435 checkAccess(REF_newInvokeSpecial, refc, ctor);
2436 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2437 if (checkSecurity)
2438 checkSecurityManager(refc, ctor);
2439 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2440 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2441 }
2442
2443 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2444 */
2445 /*non-public*/
2446 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2447 if (!(type instanceof Class || type instanceof MethodType))
2448 throw new InternalError("unresolved MemberName");
2449 MemberName member = new MemberName(refKind, defc, name, type);
2450 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2451 if (mh != null) {
2452 checkSymbolicClass(defc);
2453 return mh;
2454 }
2455 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2456 // Treat MethodHandle.invoke and invokeExact specially.
2457 mh = findVirtualForMH(member.getName(), member.getMethodType());
2458 if (mh != null) {
2459 return mh;
2460 }
2461 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
2462 // Treat signature-polymorphic methods on VarHandle specially.
2463 mh = findVirtualForVH(member.getName(), member.getMethodType());
2464 if (mh != null) {
2465 return mh;
2466 }
2467 }
2468 MemberName resolved = resolveOrFail(refKind, member);
2469 mh = getDirectMethodForConstant(refKind, defc, resolved);
2470 if (mh instanceof DirectMethodHandle
2471 && canBeCached(refKind, defc, resolved)) {
2472 MemberName key = mh.internalMemberName();
2473 if (key != null) {
2474 key = key.asNormalOriginal();
2475 }
2476 if (member.equals(key)) { // better safe than sorry
2477 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2478 }
2479 }
2480 return mh;
2481 }
2482 private
2483 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2484 if (refKind == REF_invokeSpecial) {
2485 return false;
2486 }
2487 if (!Modifier.isPublic(defc.getModifiers()) ||
2488 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2489 !member.isPublic() ||
2490 member.isCallerSensitive()) {
2491 return false;
2492 }
2493 ClassLoader loader = defc.getClassLoader();
2494 if (loader != null) {
2495 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2496 boolean found = false;
2497 while (sysl != null) {
2498 if (loader == sysl) { found = true; break; }
2499 sysl = sysl.getParent();
2500 }
2501 if (!found) {
2502 return false;
2503 }
2504 }
2505 try {
2506 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
2507 new MemberName(refKind, defc, member.getName(), member.getType()));
2508 if (resolved2 == null) {
2509 return false;
2510 }
2511 checkSecurityManager(defc, resolved2);
2512 } catch (SecurityException ex) {
2513 return false;
2514 }
2515 return true;
2516 }
2517 private
2518 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2519 throws ReflectiveOperationException {
2520 if (MethodHandleNatives.refKindIsField(refKind)) {
2521 return getDirectFieldNoSecurityManager(refKind, defc, member);
2522 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2523 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2524 } else if (refKind == REF_newInvokeSpecial) {
2525 return getDirectConstructorNoSecurityManager(defc, member);
2526 }
2527 // oops
2528 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2529 }
2530
2531 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2532 }
2533
2534 /**
2535 * Produces a method handle constructing arrays of a desired type,
2536 * as if by the {@code anewarray} bytecode.
2537 * The return type of the method handle will be the array type.
2538 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2539 *
2540 * <p> If the returned method handle is invoked with a negative
2541 * array size, a {@code NegativeArraySizeException} will be thrown.
2542 *
2543 * @param arrayClass an array type
2544 * @return a method handle which can create arrays of the given type
2545 * @throws NullPointerException if the argument is {@code null}
2546 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2547 * @see java.lang.reflect.Array#newInstance(Class, int)
2548 * @jvms 6.5 {@code anewarray} Instruction
2549 * @since 9
2550 */
2551 public static
2552 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2553 if (!arrayClass.isArray()) {
2554 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2555 }
2556 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2557 bindTo(arrayClass.getComponentType());
2558 return ani.asType(ani.type().changeReturnType(arrayClass));
2559 }
2560
2561 /**
2562 * Produces a method handle returning the length of an array,
2563 * as if by the {@code arraylength} bytecode.
2564 * The type of the method handle will have {@code int} as return type,
2565 * and its sole argument will be the array type.
2566 *
2567 * <p> If the returned method handle is invoked with a {@code null}
2568 * array reference, a {@code NullPointerException} will be thrown.
2569 *
2570 * @param arrayClass an array type
2571 * @return a method handle which can retrieve the length of an array of the given array type
2572 * @throws NullPointerException if the argument is {@code null}
2573 * @throws IllegalArgumentException if arrayClass is not an array type
2574 * @jvms 6.5 {@code arraylength} Instruction
2575 * @since 9
2576 */
2577 public static
2578 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2579 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2580 }
2581
2582 /**
2583 * Produces a method handle giving read access to elements of an array,
2584 * as if by the {@code aaload} bytecode.
2585 * The type of the method handle will have a return type of the array's
2586 * element type. Its first argument will be the array type,
2587 * and the second will be {@code int}.
2588 *
2589 * <p> When the returned method handle is invoked,
2590 * the array reference and array index are checked.
2591 * A {@code NullPointerException} will be thrown if the array reference
2592 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2593 * thrown if the index is negative or if it is greater than or equal to
2594 * the length of the array.
2595 *
2596 * @param arrayClass an array type
2597 * @return a method handle which can load values from the given array type
2598 * @throws NullPointerException if the argument is null
2599 * @throws IllegalArgumentException if arrayClass is not an array type
2600 * @jvms 6.5 {@code aaload} Instruction
2601 */
2602 public static
2603 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2604 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2605 }
2606
2607 /**
2608 * Produces a method handle giving write access to elements of an array,
2609 * as if by the {@code astore} bytecode.
2610 * The type of the method handle will have a void return type.
2611 * Its last argument will be the array's element type.
2612 * The first and second arguments will be the array type and int.
2613 *
2614 * <p> When the returned method handle is invoked,
2615 * the array reference and array index are checked.
2616 * A {@code NullPointerException} will be thrown if the array reference
2617 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2618 * thrown if the index is negative or if it is greater than or equal to
2619 * the length of the array.
2620 *
2621 * @param arrayClass the class of an array
2622 * @return a method handle which can store values into the array type
2623 * @throws NullPointerException if the argument is null
2624 * @throws IllegalArgumentException if arrayClass is not an array type
2625 * @jvms 6.5 {@code aastore} Instruction
2626 */
2627 public static
2628 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2629 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2630 }
2631
2632 /**
2633 * Produces a VarHandle giving access to elements of an array of type
2634 * {@code arrayClass}. The VarHandle's variable type is the component type
2635 * of {@code arrayClass} and the list of coordinate types is
2636 * {@code (arrayClass, int)}, where the {@code int} coordinate type
2637 * corresponds to an argument that is an index into an array.
2638 * <p>
2639 * Certain access modes of the returned VarHandle are unsupported under
2640 * the following conditions:
2641 * <ul>
2642 * <li>if the component type is anything other than {@code byte},
2643 * {@code short}, {@code char}, {@code int}, {@code long},
2644 * {@code float}, or {@code double} then numeric atomic update access
2645 * modes are unsupported.
2646 * <li>if the field type is anything other than {@code boolean},
2647 * {@code byte}, {@code short}, {@code char}, {@code int} or
2648 * {@code long} then bitwise atomic update access modes are
2649 * unsupported.
2650 * </ul>
2651 * <p>
2652 * If the component type is {@code float} or {@code double} then numeric
2653 * and atomic update access modes compare values using their bitwise
2654 * representation (see {@link Float#floatToRawIntBits} and
2655 * {@link Double#doubleToRawLongBits}, respectively).
2656 *
2657 * <p> When the returned {@code VarHandle} is invoked,
2658 * the array reference and array index are checked.
2659 * A {@code NullPointerException} will be thrown if the array reference
2660 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2661 * thrown if the index is negative or if it is greater than or equal to
2662 * the length of the array.
2663 *
2664 * @apiNote
2665 * Bitwise comparison of {@code float} values or {@code double} values,
2666 * as performed by the numeric and atomic update access modes, differ
2667 * from the primitive {@code ==} operator and the {@link Float#equals}
2668 * and {@link Double#equals} methods, specifically with respect to
2669 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2670 * Care should be taken when performing a compare and set or a compare
2671 * and exchange operation with such values since the operation may
2672 * unexpectedly fail.
2673 * There are many possible NaN values that are considered to be
2674 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2675 * provided by Java can distinguish between them. Operation failure can
2676 * occur if the expected or witness value is a NaN value and it is
2677 * transformed (perhaps in a platform specific manner) into another NaN
2678 * value, and thus has a different bitwise representation (see
2679 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2680 * details).
2681 * The values {@code -0.0} and {@code +0.0} have different bitwise
2682 * representations but are considered equal when using the primitive
2683 * {@code ==} operator. Operation failure can occur if, for example, a
2684 * numeric algorithm computes an expected value to be say {@code -0.0}
2685 * and previously computed the witness value to be say {@code +0.0}.
2686 * @param arrayClass the class of an array, of type {@code T[]}
2687 * @return a VarHandle giving access to elements of an array
2688 * @throws NullPointerException if the arrayClass is null
2689 * @throws IllegalArgumentException if arrayClass is not an array type
2690 * @since 9
2691 */
2692 public static
2693 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2694 return VarHandles.makeArrayElementHandle(arrayClass);
2695 }
2696
2697 /**
2698 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2699 * viewed as if it were a different primitive array type, such as
2700 * {@code int[]} or {@code long[]}.
2701 * The VarHandle's variable type is the component type of
2702 * {@code viewArrayClass} and the list of coordinate types is
2703 * {@code (byte[], int)}, where the {@code int} coordinate type
2704 * corresponds to an argument that is an index into a {@code byte[]} array.
2705 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
2706 * array, composing bytes to or from a value of the component type of
2707 * {@code viewArrayClass} according to the given endianness.
2708 * <p>
2709 * The supported component types (variables types) are {@code short},
2710 * {@code char}, {@code int}, {@code long}, {@code float} and
2711 * {@code double}.
2712 * <p>
2713 * Access of bytes at a given index will result in an
2714 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2715 * or greater than the {@code byte[]} array length minus the size (in bytes)
2716 * of {@code T}.
2717 * <p>
2718 * Access of bytes at an index may be aligned or misaligned for {@code T},
2719 * with respect to the underlying memory address, {@code A} say, associated
2720 * with the array and index.
2721 * If access is misaligned then access for anything other than the
2722 * {@code get} and {@code set} access modes will result in an
2723 * {@code IllegalStateException}. In such cases atomic access is only
2724 * guaranteed with respect to the largest power of two that divides the GCD
2725 * of {@code A} and the size (in bytes) of {@code T}.
2726 * If access is aligned then following access modes are supported and are
2727 * guaranteed to support atomic access:
2728 * <ul>
2729 * <li>read write access modes for all {@code T}, with the exception of
2730 * access modes {@code get} and {@code set} for {@code long} and
2731 * {@code double} on 32-bit platforms.
2732 * <li>atomic update access modes for {@code int}, {@code long},
2733 * {@code float} or {@code double}.
2734 * (Future major platform releases of the JDK may support additional
2735 * types for certain currently unsupported access modes.)
2736 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2737 * (Future major platform releases of the JDK may support additional
2738 * numeric types for certain currently unsupported access modes.)
2739 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2740 * (Future major platform releases of the JDK may support additional
2741 * numeric types for certain currently unsupported access modes.)
2742 * </ul>
2743 * <p>
2744 * Misaligned access, and therefore atomicity guarantees, may be determined
2745 * for {@code byte[]} arrays without operating on a specific array. Given
2746 * an {@code index}, {@code T} and it's corresponding boxed type,
2747 * {@code T_BOX}, misalignment may be determined as follows:
2748 * <pre>{@code
2749 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2750 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2751 * alignmentOffset(0, sizeOfT);
2752 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2753 * boolean isMisaligned = misalignedAtIndex != 0;
2754 * }</pre>
2755 * <p>
2756 * If the variable type is {@code float} or {@code double} then atomic
2757 * update access modes compare values using their bitwise representation
2758 * (see {@link Float#floatToRawIntBits} and
2759 * {@link Double#doubleToRawLongBits}, respectively).
2760 * @param viewArrayClass the view array class, with a component type of
2761 * type {@code T}
2762 * @param byteOrder the endianness of the view array elements, as
2763 * stored in the underlying {@code byte} array
2764 * @return a VarHandle giving access to elements of a {@code byte[]} array
2765 * viewed as if elements corresponding to the components type of the view
2766 * array class
2767 * @throws NullPointerException if viewArrayClass or byteOrder is null
2768 * @throws IllegalArgumentException if viewArrayClass is not an array type
2769 * @throws UnsupportedOperationException if the component type of
2770 * viewArrayClass is not supported as a variable type
2771 * @since 9
2772 */
2773 public static
2774 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2775 ByteOrder byteOrder) throws IllegalArgumentException {
2776 Objects.requireNonNull(byteOrder);
2777 return VarHandles.byteArrayViewHandle(viewArrayClass,
2778 byteOrder == ByteOrder.BIG_ENDIAN);
2779 }
2780
2781 /**
2782 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2783 * viewed as if it were an array of elements of a different primitive
2784 * component type to that of {@code byte}, such as {@code int[]} or
2785 * {@code long[]}.
2786 * The VarHandle's variable type is the component type of
2787 * {@code viewArrayClass} and the list of coordinate types is
2788 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
2789 * corresponds to an argument that is an index into a {@code byte[]} array.
2790 * The returned VarHandle accesses bytes at an index in a
2791 * {@code ByteBuffer}, composing bytes to or from a value of the component
2792 * type of {@code viewArrayClass} according to the given endianness.
2793 * <p>
2794 * The supported component types (variables types) are {@code short},
2795 * {@code char}, {@code int}, {@code long}, {@code float} and
2796 * {@code double}.
2797 * <p>
2798 * Access will result in a {@code ReadOnlyBufferException} for anything
2799 * other than the read access modes if the {@code ByteBuffer} is read-only.
2800 * <p>
2801 * Access of bytes at a given index will result in an
2802 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2803 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2804 * {@code T}.
2805 * <p>
2806 * Access of bytes at an index may be aligned or misaligned for {@code T},
2807 * with respect to the underlying memory address, {@code A} say, associated
2808 * with the {@code ByteBuffer} and index.
2809 * If access is misaligned then access for anything other than the
2810 * {@code get} and {@code set} access modes will result in an
2811 * {@code IllegalStateException}. In such cases atomic access is only
2812 * guaranteed with respect to the largest power of two that divides the GCD
2813 * of {@code A} and the size (in bytes) of {@code T}.
2814 * If access is aligned then following access modes are supported and are
2815 * guaranteed to support atomic access:
2816 * <ul>
2817 * <li>read write access modes for all {@code T}, with the exception of
2818 * access modes {@code get} and {@code set} for {@code long} and
2819 * {@code double} on 32-bit platforms.
2820 * <li>atomic update access modes for {@code int}, {@code long},
2821 * {@code float} or {@code double}.
2822 * (Future major platform releases of the JDK may support additional
2823 * types for certain currently unsupported access modes.)
2824 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2825 * (Future major platform releases of the JDK may support additional
2826 * numeric types for certain currently unsupported access modes.)
2827 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2828 * (Future major platform releases of the JDK may support additional
2829 * numeric types for certain currently unsupported access modes.)
2830 * </ul>
2831 * <p>
2832 * Misaligned access, and therefore atomicity guarantees, may be determined
2833 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2834 * {@code index}, {@code T} and it's corresponding boxed type,
2835 * {@code T_BOX}, as follows:
2836 * <pre>{@code
2837 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2838 * ByteBuffer bb = ...
2839 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2840 * boolean isMisaligned = misalignedAtIndex != 0;
2841 * }</pre>
2842 * <p>
2843 * If the variable type is {@code float} or {@code double} then atomic
2844 * update access modes compare values using their bitwise representation
2845 * (see {@link Float#floatToRawIntBits} and
2846 * {@link Double#doubleToRawLongBits}, respectively).
2847 * @param viewArrayClass the view array class, with a component type of
2848 * type {@code T}
2849 * @param byteOrder the endianness of the view array elements, as
2850 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2851 * endianness of a {@code ByteBuffer})
2852 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2853 * viewed as if elements corresponding to the components type of the view
2854 * array class
2855 * @throws NullPointerException if viewArrayClass or byteOrder is null
2856 * @throws IllegalArgumentException if viewArrayClass is not an array type
2857 * @throws UnsupportedOperationException if the component type of
2858 * viewArrayClass is not supported as a variable type
2859 * @since 9
2860 */
2861 public static
2862 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2863 ByteOrder byteOrder) throws IllegalArgumentException {
2864 Objects.requireNonNull(byteOrder);
2865 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2866 byteOrder == ByteOrder.BIG_ENDIAN);
2867 }
2868
2869
2870 /// method handle invocation (reflective style)
2871
2872 /**
2873 * Produces a method handle which will invoke any method handle of the
2874 * given {@code type}, with a given number of trailing arguments replaced by
2875 * a single trailing {@code Object[]} array.
2876 * The resulting invoker will be a method handle with the following
2877 * arguments:
2878 * <ul>
2879 * <li>a single {@code MethodHandle} target
2880 * <li>zero or more leading values (counted by {@code leadingArgCount})
2881 * <li>an {@code Object[]} array containing trailing arguments
2882 * </ul>
2883 * <p>
2884 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2885 * the indicated {@code type}.
2886 * That is, if the target is exactly of the given {@code type}, it will behave
2887 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2888 * is used to convert the target to the required {@code type}.
2889 * <p>
2890 * The type of the returned invoker will not be the given {@code type}, but rather
2891 * will have all parameters except the first {@code leadingArgCount}
2892 * replaced by a single array of type {@code Object[]}, which will be
2893 * the final parameter.
2894 * <p>
2895 * Before invoking its target, the invoker will spread the final array, apply
2896 * reference casts as necessary, and unbox and widen primitive arguments.
2897 * If, when the invoker is called, the supplied array argument does
2898 * not have the correct number of elements, the invoker will throw
2899 * an {@link IllegalArgumentException} instead of invoking the target.
2900 * <p>
2901 * This method is equivalent to the following code (though it may be more efficient):
2902 * <blockquote><pre>{@code
2903 MethodHandle invoker = MethodHandles.invoker(type);
2904 int spreadArgCount = type.parameterCount() - leadingArgCount;
2905 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2906 return invoker;
2907 * }</pre></blockquote>
2908 * This method throws no reflective or security exceptions.
2909 * @param type the desired target type
2910 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2911 * @return a method handle suitable for invoking any method handle of the given type
2912 * @throws NullPointerException if {@code type} is null
2913 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2914 * the range from 0 to {@code type.parameterCount()} inclusive,
2915 * or if the resulting method handle's type would have
2916 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2917 */
2918 public static
2919 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2920 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2921 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2922 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2923 return type.invokers().spreadInvoker(leadingArgCount);
2924 }
2925
2926 /**
2927 * Produces a special <em>invoker method handle</em> which can be used to
2928 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2929 * The resulting invoker will have a type which is
2930 * exactly equal to the desired type, except that it will accept
2931 * an additional leading argument of type {@code MethodHandle}.
2932 * <p>
2933 * This method is equivalent to the following code (though it may be more efficient):
2934 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2935 *
2936 * <p style="font-size:smaller;">
2937 * <em>Discussion:</em>
2938 * Invoker method handles can be useful when working with variable method handles
2939 * of unknown types.
2940 * For example, to emulate an {@code invokeExact} call to a variable method
2941 * handle {@code M}, extract its type {@code T},
2942 * look up the invoker method {@code X} for {@code T},
2943 * and call the invoker method, as {@code X.invoke(T, A...)}.
2944 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2945 * is unknown.)
2946 * If spreading, collecting, or other argument transformations are required,
2947 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2948 * method handle values, as long as they are compatible with the type of {@code X}.
2949 * <p style="font-size:smaller;">
2950 * <em>(Note: The invoker method is not available via the Core Reflection API.
2951 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2952 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2953 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2954 * <p>
2955 * This method throws no reflective or security exceptions.
2956 * @param type the desired target type
2957 * @return a method handle suitable for invoking any method handle of the given type
2958 * @throws IllegalArgumentException if the resulting method handle's type would have
2959 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2960 */
2961 public static
2962 MethodHandle exactInvoker(MethodType type) {
2963 return type.invokers().exactInvoker();
2964 }
2965
2966 /**
2967 * Produces a special <em>invoker method handle</em> which can be used to
2968 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2969 * The resulting invoker will have a type which is
2970 * exactly equal to the desired type, except that it will accept
2971 * an additional leading argument of type {@code MethodHandle}.
2972 * <p>
2973 * Before invoking its target, if the target differs from the expected type,
2974 * the invoker will apply reference casts as
2975 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2976 * Similarly, the return value will be converted as necessary.
2977 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2978 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2979 * <p>
2980 * This method is equivalent to the following code (though it may be more efficient):
2981 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2982 * <p style="font-size:smaller;">
2983 * <em>Discussion:</em>
2984 * A {@linkplain MethodType#genericMethodType general method type} is one which
2985 * mentions only {@code Object} arguments and return values.
2986 * An invoker for such a type is capable of calling any method handle
2987 * of the same arity as the general type.
2988 * <p style="font-size:smaller;">
2989 * <em>(Note: The invoker method is not available via the Core Reflection API.
2990 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2991 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2992 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2993 * <p>
2994 * This method throws no reflective or security exceptions.
2995 * @param type the desired target type
2996 * @return a method handle suitable for invoking any method handle convertible to the given type
2997 * @throws IllegalArgumentException if the resulting method handle's type would have
2998 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2999 */
3000 public static
3001 MethodHandle invoker(MethodType type) {
3002 return type.invokers().genericInvoker();
3003 }
3004
3005 /**
3006 * Produces a special <em>invoker method handle</em> which can be used to
3007 * invoke a signature-polymorphic access mode method on any VarHandle whose
3008 * associated access mode type is compatible with the given type.
3009 * The resulting invoker will have a type which is exactly equal to the
3010 * desired given type, except that it will accept an additional leading
3011 * argument of type {@code VarHandle}.
3012 *
3013 * @param accessMode the VarHandle access mode
3014 * @param type the desired target type
3015 * @return a method handle suitable for invoking an access mode method of
3016 * any VarHandle whose access mode type is of the given type.
3017 * @since 9
3018 */
3019 static public
3020 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3021 return type.invokers().varHandleMethodExactInvoker(accessMode);
3022 }
3023
3024 /**
3025 * Produces a special <em>invoker method handle</em> which can be used to
3026 * invoke a signature-polymorphic access mode method on any VarHandle whose
3027 * associated access mode type is compatible with the given type.
3028 * The resulting invoker will have a type which is exactly equal to the
3029 * desired given type, except that it will accept an additional leading
3030 * argument of type {@code VarHandle}.
3031 * <p>
3032 * Before invoking its target, if the access mode type differs from the
3033 * desired given type, the invoker will apply reference casts as necessary
3034 * and box, unbox, or widen primitive values, as if by
3035 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3036 * converted as necessary.
3037 * <p>
3038 * This method is equivalent to the following code (though it may be more
3039 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3040 *
3041 * @param accessMode the VarHandle access mode
3042 * @param type the desired target type
3043 * @return a method handle suitable for invoking an access mode method of
3044 * any VarHandle whose access mode type is convertible to the given
3045 * type.
3046 * @since 9
3047 */
3048 static public
3049 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3050 return type.invokers().varHandleMethodInvoker(accessMode);
3051 }
3052
3053 static /*non-public*/
3054 MethodHandle basicInvoker(MethodType type) {
3055 return type.invokers().basicInvoker();
3056 }
3057
3058 /// method handle modification (creation from other method handles)
3059
3060 /**
3061 * Produces a method handle which adapts the type of the
3062 * given method handle to a new type by pairwise argument and return type conversion.
3063 * The original type and new type must have the same number of arguments.
3064 * The resulting method handle is guaranteed to report a type
3065 * which is equal to the desired new type.
3066 * <p>
3067 * If the original type and new type are equal, returns target.
3068 * <p>
3069 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3070 * and some additional conversions are also applied if those conversions fail.
3071 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3072 * if possible, before or instead of any conversions done by {@code asType}:
3073 * <ul>
3074 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3075 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3076 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3077 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3078 * the boolean is converted to a byte value, 1 for true, 0 for false.
3079 * (This treatment follows the usage of the bytecode verifier.)
3080 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3081 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3082 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3083 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3084 * then a Java casting conversion (JLS 5.5) is applied.
3085 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3086 * widening and/or narrowing.)
3087 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3088 * conversion will be applied at runtime, possibly followed
3089 * by a Java casting conversion (JLS 5.5) on the primitive value,
3090 * possibly followed by a conversion from byte to boolean by testing
3091 * the low-order bit.
3092 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3093 * and if the reference is null at runtime, a zero value is introduced.
3094 * </ul>
3095 * @param target the method handle to invoke after arguments are retyped
3096 * @param newType the expected type of the new method handle
3097 * @return a method handle which delegates to the target after performing
3098 * any necessary argument conversions, and arranges for any
3099 * necessary return value conversions
3100 * @throws NullPointerException if either argument is null
3101 * @throws WrongMethodTypeException if the conversion cannot be made
3102 * @see MethodHandle#asType
3103 */
3104 public static
3105 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3106 explicitCastArgumentsChecks(target, newType);
3107 // use the asTypeCache when possible:
3108 MethodType oldType = target.type();
3109 if (oldType == newType) return target;
3110 if (oldType.explicitCastEquivalentToAsType(newType)) {
3111 return target.asFixedArity().asType(newType);
3112 }
3113 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3114 }
3115
3116 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3117 if (target.type().parameterCount() != newType.parameterCount()) {
3118 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3119 }
3120 }
3121
3122 /**
3123 * Produces a method handle which adapts the calling sequence of the
3124 * given method handle to a new type, by reordering the arguments.
3125 * The resulting method handle is guaranteed to report a type
3126 * which is equal to the desired new type.
3127 * <p>
3128 * The given array controls the reordering.
3129 * Call {@code #I} the number of incoming parameters (the value
3130 * {@code newType.parameterCount()}, and call {@code #O} the number
3131 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3132 * Then the length of the reordering array must be {@code #O},
3133 * and each element must be a non-negative number less than {@code #I}.
3134 * For every {@code N} less than {@code #O}, the {@code N}-th
3135 * outgoing argument will be taken from the {@code I}-th incoming
3136 * argument, where {@code I} is {@code reorder[N]}.
3137 * <p>
3138 * No argument or return value conversions are applied.
3139 * The type of each incoming argument, as determined by {@code newType},
3140 * must be identical to the type of the corresponding outgoing parameter
3141 * or parameters in the target method handle.
3142 * The return type of {@code newType} must be identical to the return
3143 * type of the original target.
3144 * <p>
3145 * The reordering array need not specify an actual permutation.
3146 * An incoming argument will be duplicated if its index appears
3147 * more than once in the array, and an incoming argument will be dropped
3148 * if its index does not appear in the array.
3149 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3150 * incoming arguments which are not mentioned in the reordering array
3151 * may be of any type, as determined only by {@code newType}.
3152 * <blockquote><pre>{@code
3153 import static java.lang.invoke.MethodHandles.*;
3154 import static java.lang.invoke.MethodType.*;
3155 ...
3156 MethodType intfn1 = methodType(int.class, int.class);
3157 MethodType intfn2 = methodType(int.class, int.class, int.class);
3158 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3159 assert(sub.type().equals(intfn2));
3160 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3161 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3162 assert((int)rsub.invokeExact(1, 100) == 99);
3163 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3164 assert(add.type().equals(intfn2));
3165 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3166 assert(twice.type().equals(intfn1));
3167 assert((int)twice.invokeExact(21) == 42);
3168 * }</pre></blockquote>
3169 * <p>
3170 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3171 * variable-arity method handle}, even if the original target method handle was.
3172 * @param target the method handle to invoke after arguments are reordered
3173 * @param newType the expected type of the new method handle
3174 * @param reorder an index array which controls the reordering
3175 * @return a method handle which delegates to the target after it
3176 * drops unused arguments and moves and/or duplicates the other arguments
3177 * @throws NullPointerException if any argument is null
3178 * @throws IllegalArgumentException if the index array length is not equal to
3179 * the arity of the target, or if any index array element
3180 * not a valid index for a parameter of {@code newType},
3181 * or if two corresponding parameter types in
3182 * {@code target.type()} and {@code newType} are not identical,
3183 */
3184 public static
3185 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3186 reorder = reorder.clone(); // get a private copy
3187 MethodType oldType = target.type();
3188 permuteArgumentChecks(reorder, newType, oldType);
3189 // first detect dropped arguments and handle them separately
3190 int[] originalReorder = reorder;
3191 BoundMethodHandle result = target.rebind();
3192 LambdaForm form = result.form;
3193 int newArity = newType.parameterCount();
3194 // Normalize the reordering into a real permutation,
3195 // by removing duplicates and adding dropped elements.
3196 // This somewhat improves lambda form caching, as well
3197 // as simplifying the transform by breaking it up into steps.
3198 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3199 if (ddIdx > 0) {
3200 // We found a duplicated entry at reorder[ddIdx].
3201 // Example: (x,y,z)->asList(x,y,z)
3202 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3203 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3204 // The starred element corresponds to the argument
3205 // deleted by the dupArgumentForm transform.
3206 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3207 boolean killFirst = false;
3208 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3209 // Set killFirst if the dup is larger than an intervening position.
3210 // This will remove at least one inversion from the permutation.
3211 if (dupVal > val) killFirst = true;
3212 }
3213 if (!killFirst) {
3214 srcPos = dstPos;
3215 dstPos = ddIdx;
3216 }
3217 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3218 assert (reorder[srcPos] == reorder[dstPos]);
3219 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3220 // contract the reordering by removing the element at dstPos
3221 int tailPos = dstPos + 1;
3222 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3223 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3224 } else {
3225 int dropVal = ~ddIdx, insPos = 0;
3226 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3227 // Find first element of reorder larger than dropVal.
3228 // This is where we will insert the dropVal.
3229 insPos += 1;
3230 }
3231 Class<?> ptype = newType.parameterType(dropVal);
3232 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3233 oldType = oldType.insertParameterTypes(insPos, ptype);
3234 // expand the reordering by inserting an element at insPos
3235 int tailPos = insPos + 1;
3236 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3237 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3238 reorder[insPos] = dropVal;
3239 }
3240 assert (permuteArgumentChecks(reorder, newType, oldType));
3241 }
3242 assert (reorder.length == newArity); // a perfect permutation
3243 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3244 form = form.editor().permuteArgumentsForm(1, reorder);
3245 if (newType == result.type() && form == result.internalForm())
3246 return result;
3247 return result.copyWith(newType, form);
3248 }
3249
3250 /**
3251 * Return an indication of any duplicate or omission in reorder.
3252 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3253 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3254 * Otherwise, return zero.
3255 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3256 */
3257 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3258 final int BIT_LIMIT = 63; // max number of bits in bit mask
3259 if (newArity < BIT_LIMIT) {
3260 long mask = 0;
3261 for (int i = 0; i < reorder.length; i++) {
3262 int arg = reorder[i];
3263 if (arg >= newArity) {
3264 return reorder.length;
3265 }
3266 long bit = 1L << arg;
3267 if ((mask & bit) != 0) {
3268 return i; // >0 indicates a dup
3269 }
3270 mask |= bit;
3271 }
3272 if (mask == (1L << newArity) - 1) {
3273 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3274 return 0;
3275 }
3276 // find first zero
3277 long zeroBit = Long.lowestOneBit(~mask);
3278 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3279 assert(zeroPos <= newArity);
3280 if (zeroPos == newArity) {
3281 return 0;
3282 }
3283 return ~zeroPos;
3284 } else {
3285 // same algorithm, different bit set
3286 BitSet mask = new BitSet(newArity);
3287 for (int i = 0; i < reorder.length; i++) {
3288 int arg = reorder[i];
3289 if (arg >= newArity) {
3290 return reorder.length;
3291 }
3292 if (mask.get(arg)) {
3293 return i; // >0 indicates a dup
3294 }
3295 mask.set(arg);
3296 }
3297 int zeroPos = mask.nextClearBit(0);
3298 assert(zeroPos <= newArity);
3299 if (zeroPos == newArity) {
3300 return 0;
3301 }
3302 return ~zeroPos;
3303 }
3304 }
3305
3306 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3307 if (newType.returnType() != oldType.returnType())
3308 throw newIllegalArgumentException("return types do not match",
3309 oldType, newType);
3310 if (reorder.length == oldType.parameterCount()) {
3311 int limit = newType.parameterCount();
3312 boolean bad = false;
3313 for (int j = 0; j < reorder.length; j++) {
3314 int i = reorder[j];
3315 if (i < 0 || i >= limit) {
3316 bad = true; break;
3317 }
3318 Class<?> src = newType.parameterType(i);
3319 Class<?> dst = oldType.parameterType(j);
3320 if (src != dst)
3321 throw newIllegalArgumentException("parameter types do not match after reorder",
3322 oldType, newType);
3323 }
3324 if (!bad) return true;
3325 }
3326 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3327 }
3328
3329 /**
3330 * Produces a method handle of the requested return type which returns the given
3331 * constant value every time it is invoked.
3332 * <p>
3333 * Before the method handle is returned, the passed-in value is converted to the requested type.
3334 * If the requested type is primitive, widening primitive conversions are attempted,
3335 * else reference conversions are attempted.
3336 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3337 * @param type the return type of the desired method handle
3338 * @param value the value to return
3339 * @return a method handle of the given return type and no arguments, which always returns the given value
3340 * @throws NullPointerException if the {@code type} argument is null
3341 * @throws ClassCastException if the value cannot be converted to the required return type
3342 * @throws IllegalArgumentException if the given type is {@code void.class}
3343 */
3344 public static
3345 MethodHandle constant(Class<?> type, Object value) {
3346 if (type.isPrimitive()) {
3347 if (type == void.class)
3348 throw newIllegalArgumentException("void type");
3349 Wrapper w = Wrapper.forPrimitiveType(type);
3350 value = w.convert(value, type);
3351 if (w.zero().equals(value))
3352 return zero(w, type);
3353 return insertArguments(identity(type), 0, value);
3354 } else {
3355 if (value == null)
3356 return zero(Wrapper.OBJECT, type);
3357 return identity(type).bindTo(value);
3358 }
3359 }
3360
3361 /**
3362 * Produces a method handle which returns its sole argument when invoked.
3363 * @param type the type of the sole parameter and return value of the desired method handle
3364 * @return a unary method handle which accepts and returns the given type
3365 * @throws NullPointerException if the argument is null
3366 * @throws IllegalArgumentException if the given type is {@code void.class}
3367 */
3368 public static
3369 MethodHandle identity(Class<?> type) {
3370 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3371 int pos = btw.ordinal();
3372 MethodHandle ident = IDENTITY_MHS[pos];
3373 if (ident == null) {
3374 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3375 }
3376 if (ident.type().returnType() == type)
3377 return ident;
3378 // something like identity(Foo.class); do not bother to intern these
3379 assert (btw == Wrapper.OBJECT);
3380 return makeIdentity(type);
3381 }
3382
3383 /**
3384 * Produces a constant method handle of the requested return type which
3385 * returns the default value for that type every time it is invoked.
3386 * The resulting constant method handle will have no side effects.
3387 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3388 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3389 * since {@code explicitCastArguments} converts {@code null} to default values.
3390 * @param type the expected return type of the desired method handle
3391 * @return a constant method handle that takes no arguments
3392 * and returns the default value of the given type (or void, if the type is void)
3393 * @throws NullPointerException if the argument is null
3394 * @see MethodHandles#constant
3395 * @see MethodHandles#empty
3396 * @see MethodHandles#explicitCastArguments
3397 * @since 9
3398 */
3399 public static MethodHandle zero(Class<?> type) {
3400 Objects.requireNonNull(type);
3401 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3402 }
3403
3404 private static MethodHandle identityOrVoid(Class<?> type) {
3405 return type == void.class ? zero(type) : identity(type);
3406 }
3407
3408 /**
3409 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3410 * and returns a suitable default depending on the return type.
3411 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3412 * <p>The returned method handle is equivalent to
3413 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3414 *
3415 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3416 * {@code guardWithTest(pred, target, empty(target.type())}.
3417 * @param type the type of the desired method handle
3418 * @return a constant method handle of the given type, which returns a default value of the given return type
3419 * @throws NullPointerException if the argument is null
3420 * @see MethodHandles#zero
3421 * @see MethodHandles#constant
3422 * @since 9
3423 */
3424 public static MethodHandle empty(MethodType type) {
3425 Objects.requireNonNull(type);
3426 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3427 }
3428
3429 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3430 private static MethodHandle makeIdentity(Class<?> ptype) {
3431 MethodType mtype = methodType(ptype, ptype);
3432 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3433 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3434 }
3435
3436 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3437 int pos = btw.ordinal();
3438 MethodHandle zero = ZERO_MHS[pos];
3439 if (zero == null) {
3440 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3441 }
3442 if (zero.type().returnType() == rtype)
3443 return zero;
3444 assert(btw == Wrapper.OBJECT);
3445 return makeZero(rtype);
3446 }
3447 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3448 private static MethodHandle makeZero(Class<?> rtype) {
3449 MethodType mtype = methodType(rtype);
3450 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3451 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3452 }
3453
3454 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3455 // Simulate a CAS, to avoid racy duplication of results.
3456 MethodHandle prev = cache[pos];
3457 if (prev != null) return prev;
3458 return cache[pos] = value;
3459 }
3460
3461 /**
3462 * Provides a target method handle with one or more <em>bound arguments</em>
3463 * in advance of the method handle's invocation.
3464 * The formal parameters to the target corresponding to the bound
3465 * arguments are called <em>bound parameters</em>.
3466 * Returns a new method handle which saves away the bound arguments.
3467 * When it is invoked, it receives arguments for any non-bound parameters,
3468 * binds the saved arguments to their corresponding parameters,
3469 * and calls the original target.
3470 * <p>
3471 * The type of the new method handle will drop the types for the bound
3472 * parameters from the original target type, since the new method handle
3473 * will no longer require those arguments to be supplied by its callers.
3474 * <p>
3475 * Each given argument object must match the corresponding bound parameter type.
3476 * If a bound parameter type is a primitive, the argument object
3477 * must be a wrapper, and will be unboxed to produce the primitive value.
3478 * <p>
3479 * The {@code pos} argument selects which parameters are to be bound.
3480 * It may range between zero and <i>N-L</i> (inclusively),
3481 * where <i>N</i> is the arity of the target method handle
3482 * and <i>L</i> is the length of the values array.
3483 * <p>
3484 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3485 * variable-arity method handle}, even if the original target method handle was.
3486 * @param target the method handle to invoke after the argument is inserted
3487 * @param pos where to insert the argument (zero for the first)
3488 * @param values the series of arguments to insert
3489 * @return a method handle which inserts an additional argument,
3490 * before calling the original method handle
3491 * @throws NullPointerException if the target or the {@code values} array is null
3492 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
3493 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
3494 * is the length of the values array.
3495 * @throws ClassCastException if an argument does not match the corresponding bound parameter
3496 * type.
3497 * @see MethodHandle#bindTo
3498 */
3499 public static
3500 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3501 int insCount = values.length;
3502 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3503 if (insCount == 0) return target;
3504 BoundMethodHandle result = target.rebind();
3505 for (int i = 0; i < insCount; i++) {
3506 Object value = values[i];
3507 Class<?> ptype = ptypes[pos+i];
3508 if (ptype.isPrimitive()) {
3509 result = insertArgumentPrimitive(result, pos, ptype, value);
3510 } else {
3511 value = ptype.cast(value); // throw CCE if needed
3512 result = result.bindArgumentL(pos, value);
3513 }
3514 }
3515 return result;
3516 }
3517
3518 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3519 Class<?> ptype, Object value) {
3520 Wrapper w = Wrapper.forPrimitiveType(ptype);
3521 // perform unboxing and/or primitive conversion
3522 value = w.convert(value, ptype);
3523 switch (w) {
3524 case INT: return result.bindArgumentI(pos, (int)value);
3525 case LONG: return result.bindArgumentJ(pos, (long)value);
3526 case FLOAT: return result.bindArgumentF(pos, (float)value);
3527 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3528 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3529 }
3530 }
3531
3532 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3533 MethodType oldType = target.type();
3534 int outargs = oldType.parameterCount();
3535 int inargs = outargs - insCount;
3536 if (inargs < 0)
3537 throw newIllegalArgumentException("too many values to insert");
3538 if (pos < 0 || pos > inargs)
3539 throw newIllegalArgumentException("no argument type to append");
3540 return oldType.ptypes();
3541 }
3542
3543 /**
3544 * Produces a method handle which will discard some dummy arguments
3545 * before calling some other specified <i>target</i> method handle.
3546 * The type of the new method handle will be the same as the target's type,
3547 * except it will also include the dummy argument types,
3548 * at some given position.
3549 * <p>
3550 * The {@code pos} argument may range between zero and <i>N</i>,
3551 * where <i>N</i> is the arity of the target.
3552 * If {@code pos} is zero, the dummy arguments will precede
3553 * the target's real arguments; if {@code pos} is <i>N</i>
3554 * they will come after.
3555 * <p>
3556 * <b>Example:</b>
3557 * <blockquote><pre>{@code
3558 import static java.lang.invoke.MethodHandles.*;
3559 import static java.lang.invoke.MethodType.*;
3560 ...
3561 MethodHandle cat = lookup().findVirtual(String.class,
3562 "concat", methodType(String.class, String.class));
3563 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3564 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3565 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3566 assertEquals(bigType, d0.type());
3567 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3568 * }</pre></blockquote>
3569 * <p>
3570 * This method is also equivalent to the following code:
3571 * <blockquote><pre>
3572 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3573 * </pre></blockquote>
3574 * @param target the method handle to invoke after the arguments are dropped
3575 * @param valueTypes the type(s) of the argument(s) to drop
3576 * @param pos position of first argument to drop (zero for the leftmost)
3577 * @return a method handle which drops arguments of the given types,
3578 * before calling the original method handle
3579 * @throws NullPointerException if the target is null,
3580 * or if the {@code valueTypes} list or any of its elements is null
3581 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3582 * or if {@code pos} is negative or greater than the arity of the target,
3583 * or if the new method handle's type would have too many parameters
3584 */
3585 public static
3586 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3587 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3588 }
3589
3590 private static List<Class<?>> copyTypes(Object[] array) {
3591 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3592 }
3593
3594 private static
3595 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3596 MethodType oldType = target.type(); // get NPE
3597 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3598 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3599 if (dropped == 0) return target;
3600 BoundMethodHandle result = target.rebind();
3601 LambdaForm lform = result.form;
3602 int insertFormArg = 1 + pos;
3603 for (Class<?> ptype : valueTypes) {
3604 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3605 }
3606 result = result.copyWith(newType, lform);
3607 return result;
3608 }
3609
3610 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3611 int dropped = valueTypes.size();
3612 MethodType.checkSlotCount(dropped);
3613 int outargs = oldType.parameterCount();
3614 int inargs = outargs + dropped;
3615 if (pos < 0 || pos > outargs)
3616 throw newIllegalArgumentException("no argument type to remove"
3617 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3618 );
3619 return dropped;
3620 }
3621
3622 /**
3623 * Produces a method handle which will discard some dummy arguments
3624 * before calling some other specified <i>target</i> method handle.
3625 * The type of the new method handle will be the same as the target's type,
3626 * except it will also include the dummy argument types,
3627 * at some given position.
3628 * <p>
3629 * The {@code pos} argument may range between zero and <i>N</i>,
3630 * where <i>N</i> is the arity of the target.
3631 * If {@code pos} is zero, the dummy arguments will precede
3632 * the target's real arguments; if {@code pos} is <i>N</i>
3633 * they will come after.
3634 * @apiNote
3635 * <blockquote><pre>{@code
3636 import static java.lang.invoke.MethodHandles.*;
3637 import static java.lang.invoke.MethodType.*;
3638 ...
3639 MethodHandle cat = lookup().findVirtual(String.class,
3640 "concat", methodType(String.class, String.class));
3641 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3642 MethodHandle d0 = dropArguments(cat, 0, String.class);
3643 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3644 MethodHandle d1 = dropArguments(cat, 1, String.class);
3645 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3646 MethodHandle d2 = dropArguments(cat, 2, String.class);
3647 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3648 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3649 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3650 * }</pre></blockquote>
3651 * <p>
3652 * This method is also equivalent to the following code:
3653 * <blockquote><pre>
3654 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3655 * </pre></blockquote>
3656 * @param target the method handle to invoke after the arguments are dropped
3657 * @param valueTypes the type(s) of the argument(s) to drop
3658 * @param pos position of first argument to drop (zero for the leftmost)
3659 * @return a method handle which drops arguments of the given types,
3660 * before calling the original method handle
3661 * @throws NullPointerException if the target is null,
3662 * or if the {@code valueTypes} array or any of its elements is null
3663 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3664 * or if {@code pos} is negative or greater than the arity of the target,
3665 * or if the new method handle's type would have
3666 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3667 */
3668 public static
3669 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3670 return dropArguments0(target, pos, copyTypes(valueTypes));
3671 }
3672
3673 // private version which allows caller some freedom with error handling
3674 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3675 boolean nullOnFailure) {
3676 newTypes = copyTypes(newTypes.toArray());
3677 List<Class<?>> oldTypes = target.type().parameterList();
3678 int match = oldTypes.size();
3679 if (skip != 0) {
3680 if (skip < 0 || skip > match) {
3681 throw newIllegalArgumentException("illegal skip", skip, target);
3682 }
3683 oldTypes = oldTypes.subList(skip, match);
3684 match -= skip;
3685 }
3686 List<Class<?>> addTypes = newTypes;
3687 int add = addTypes.size();
3688 if (pos != 0) {
3689 if (pos < 0 || pos > add) {
3690 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3691 }
3692 addTypes = addTypes.subList(pos, add);
3693 add -= pos;
3694 assert(addTypes.size() == add);
3695 }
3696 // Do not add types which already match the existing arguments.
3697 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3698 if (nullOnFailure) {
3699 return null;
3700 }
3701 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3702 }
3703 addTypes = addTypes.subList(match, add);
3704 add -= match;
3705 assert(addTypes.size() == add);
3706 // newTypes: ( P*[pos], M*[match], A*[add] )
3707 // target: ( S*[skip], M*[match] )
3708 MethodHandle adapter = target;
3709 if (add > 0) {
3710 adapter = dropArguments0(adapter, skip+ match, addTypes);
3711 }
3712 // adapter: (S*[skip], M*[match], A*[add] )
3713 if (pos > 0) {
3714 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3715 }
3716 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3717 return adapter;
3718 }
3719
3720 /**
3721 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3722 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3723 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3724 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3725 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3726 * {@link #dropArguments(MethodHandle, int, Class[])}.
3727 * <p>
3728 * The resulting handle will have the same return type as the target handle.
3729 * <p>
3730 * In more formal terms, assume these two type lists:<ul>
3731 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3732 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3733 * {@code newTypes}.
3734 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3735 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3736 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3737 * sub-list.
3738 * </ul>
3739 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3740 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3741 * {@link #dropArguments(MethodHandle, int, Class[])}.
3742 *
3743 * @apiNote
3744 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3745 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3746 * <blockquote><pre>{@code
3747 import static java.lang.invoke.MethodHandles.*;
3748 import static java.lang.invoke.MethodType.*;
3749 ...
3750 ...
3751 MethodHandle h0 = constant(boolean.class, true);
3752 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3753 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3754 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3755 if (h1.type().parameterCount() < h2.type().parameterCount())
3756 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3757 else
3758 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3759 MethodHandle h3 = guardWithTest(h0, h1, h2);
3760 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3761 * }</pre></blockquote>
3762 * @param target the method handle to adapt
3763 * @param skip number of targets parameters to disregard (they will be unchanged)
3764 * @param newTypes the list of types to match {@code target}'s parameter type list to
3765 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3766 * @return a possibly adapted method handle
3767 * @throws NullPointerException if either argument is null
3768 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3769 * or if {@code skip} is negative or greater than the arity of the target,
3770 * or if {@code pos} is negative or greater than the newTypes list size,
3771 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3772 * {@code pos}.
3773 * @since 9
3774 */
3775 public static
3776 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3777 Objects.requireNonNull(target);
3778 Objects.requireNonNull(newTypes);
3779 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3780 }
3781
3782 /**
3783 * Adapts a target method handle by pre-processing
3784 * one or more of its arguments, each with its own unary filter function,
3785 * and then calling the target with each pre-processed argument
3786 * replaced by the result of its corresponding filter function.
3787 * <p>
3788 * The pre-processing is performed by one or more method handles,
3789 * specified in the elements of the {@code filters} array.
3790 * The first element of the filter array corresponds to the {@code pos}
3791 * argument of the target, and so on in sequence.
3792 * The filter functions are invoked in left to right order.
3793 * <p>
3794 * Null arguments in the array are treated as identity functions,
3795 * and the corresponding arguments left unchanged.
3796 * (If there are no non-null elements in the array, the original target is returned.)
3797 * Each filter is applied to the corresponding argument of the adapter.
3798 * <p>
3799 * If a filter {@code F} applies to the {@code N}th argument of
3800 * the target, then {@code F} must be a method handle which
3801 * takes exactly one argument. The type of {@code F}'s sole argument
3802 * replaces the corresponding argument type of the target
3803 * in the resulting adapted method handle.
3804 * The return type of {@code F} must be identical to the corresponding
3805 * parameter type of the target.
3806 * <p>
3807 * It is an error if there are elements of {@code filters}
3808 * (null or not)
3809 * which do not correspond to argument positions in the target.
3810 * <p><b>Example:</b>
3811 * <blockquote><pre>{@code
3812 import static java.lang.invoke.MethodHandles.*;
3813 import static java.lang.invoke.MethodType.*;
3814 ...
3815 MethodHandle cat = lookup().findVirtual(String.class,
3816 "concat", methodType(String.class, String.class));
3817 MethodHandle upcase = lookup().findVirtual(String.class,
3818 "toUpperCase", methodType(String.class));
3819 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3820 MethodHandle f0 = filterArguments(cat, 0, upcase);
3821 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3822 MethodHandle f1 = filterArguments(cat, 1, upcase);
3823 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3824 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3825 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3826 * }</pre></blockquote>
3827 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3828 * denotes the return type of both the {@code target} and resulting adapter.
3829 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3830 * of the parameters and arguments that precede and follow the filter position
3831 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3832 * values of the filtered parameters and arguments; they also represent the
3833 * return types of the {@code filter[i]} handles. The latter accept arguments
3834 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3835 * the resulting adapter.
3836 * <blockquote><pre>{@code
3837 * T target(P... p, A[i]... a[i], B... b);
3838 * A[i] filter[i](V[i]);
3839 * T adapter(P... p, V[i]... v[i], B... b) {
3840 * return target(p..., filter[i](v[i])..., b...);
3841 * }
3842 * }</pre></blockquote>
3843 * <p>
3844 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3845 * variable-arity method handle}, even if the original target method handle was.
3846 *
3847 * @param target the method handle to invoke after arguments are filtered
3848 * @param pos the position of the first argument to filter
3849 * @param filters method handles to call initially on filtered arguments
3850 * @return method handle which incorporates the specified argument filtering logic
3851 * @throws NullPointerException if the target is null
3852 * or if the {@code filters} array is null
3853 * @throws IllegalArgumentException if a non-null element of {@code filters}
3854 * does not match a corresponding argument type of target as described above,
3855 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3856 * or if the resulting method handle's type would have
3857 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3858 */
3859 public static
3860 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3861 filterArgumentsCheckArity(target, pos, filters);
3862 MethodHandle adapter = target;
3863 // process filters in reverse order so that the invocation of
3864 // the resulting adapter will invoke the filters in left-to-right order
3865 for (int i = filters.length - 1; i >= 0; --i) {
3866 MethodHandle filter = filters[i];
3867 if (filter == null) continue; // ignore null elements of filters
3868 adapter = filterArgument(adapter, pos + i, filter);
3869 }
3870 return adapter;
3871 }
3872
3873 /*non-public*/ static
3874 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3875 filterArgumentChecks(target, pos, filter);
3876 MethodType targetType = target.type();
3877 MethodType filterType = filter.type();
3878 BoundMethodHandle result = target.rebind();
3879 Class<?> newParamType = filterType.parameterType(0);
3880 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3881 MethodType newType = targetType.changeParameterType(pos, newParamType);
3882 result = result.copyWithExtendL(newType, lform, filter);
3883 return result;
3884 }
3885
3886 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3887 MethodType targetType = target.type();
3888 int maxPos = targetType.parameterCount();
3889 if (pos + filters.length > maxPos)
3890 throw newIllegalArgumentException("too many filters");
3891 }
3892
3893 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3894 MethodType targetType = target.type();
3895 MethodType filterType = filter.type();
3896 if (filterType.parameterCount() != 1
3897 || filterType.returnType() != targetType.parameterType(pos))
3898 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3899 }
3900
3901 /**
3902 * Adapts a target method handle by pre-processing
3903 * a sub-sequence of its arguments with a filter (another method handle).
3904 * The pre-processed arguments are replaced by the result (if any) of the
3905 * filter function.
3906 * The target is then called on the modified (usually shortened) argument list.
3907 * <p>
3908 * If the filter returns a value, the target must accept that value as
3909 * its argument in position {@code pos}, preceded and/or followed by
3910 * any arguments not passed to the filter.
3911 * If the filter returns void, the target must accept all arguments
3912 * not passed to the filter.
3913 * No arguments are reordered, and a result returned from the filter
3914 * replaces (in order) the whole subsequence of arguments originally
3915 * passed to the adapter.
3916 * <p>
3917 * The argument types (if any) of the filter
3918 * replace zero or one argument types of the target, at position {@code pos},
3919 * in the resulting adapted method handle.
3920 * The return type of the filter (if any) must be identical to the
3921 * argument type of the target at position {@code pos}, and that target argument
3922 * is supplied by the return value of the filter.
3923 * <p>
3924 * In all cases, {@code pos} must be greater than or equal to zero, and
3925 * {@code pos} must also be less than or equal to the target's arity.
3926 * <p><b>Example:</b>
3927 * <blockquote><pre>{@code
3928 import static java.lang.invoke.MethodHandles.*;
3929 import static java.lang.invoke.MethodType.*;
3930 ...
3931 MethodHandle deepToString = publicLookup()
3932 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3933
3934 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3935 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3936
3937 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3938 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3939
3940 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3941 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3942 assertEquals("[top, [up, down], strange]",
3943 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3944
3945 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3946 assertEquals("[top, [up, down], [strange]]",
3947 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3948
3949 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3950 assertEquals("[top, [[up, down, strange], charm], bottom]",
3951 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3952 * }</pre></blockquote>
3953 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3954 * represents the return type of the {@code target} and resulting adapter.
3955 * {@code V}/{@code v} stand for the return type and value of the
3956 * {@code filter}, which are also found in the signature and arguments of
3957 * the {@code target}, respectively, unless {@code V} is {@code void}.
3958 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3959 * and values preceding and following the collection position, {@code pos},
3960 * in the {@code target}'s signature. They also turn up in the resulting
3961 * adapter's signature and arguments, where they surround
3962 * {@code B}/{@code b}, which represent the parameter types and arguments
3963 * to the {@code filter} (if any).
3964 * <blockquote><pre>{@code
3965 * T target(A...,V,C...);
3966 * V filter(B...);
3967 * T adapter(A... a,B... b,C... c) {
3968 * V v = filter(b...);
3969 * return target(a...,v,c...);
3970 * }
3971 * // and if the filter has no arguments:
3972 * T target2(A...,V,C...);
3973 * V filter2();
3974 * T adapter2(A... a,C... c) {
3975 * V v = filter2();
3976 * return target2(a...,v,c...);
3977 * }
3978 * // and if the filter has a void return:
3979 * T target3(A...,C...);
3980 * void filter3(B...);
3981 * T adapter3(A... a,B... b,C... c) {
3982 * filter3(b...);
3983 * return target3(a...,c...);
3984 * }
3985 * }</pre></blockquote>
3986 * <p>
3987 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3988 * one which first "folds" the affected arguments, and then drops them, in separate
3989 * steps as follows:
3990 * <blockquote><pre>{@code
3991 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3992 * mh = MethodHandles.foldArguments(mh, coll); //step 1
3993 * }</pre></blockquote>
3994 * If the target method handle consumes no arguments besides than the result
3995 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
3996 * is equivalent to {@code filterReturnValue(coll, mh)}.
3997 * If the filter method handle {@code coll} consumes one argument and produces
3998 * a non-void result, then {@code collectArguments(mh, N, coll)}
3999 * is equivalent to {@code filterArguments(mh, N, coll)}.
4000 * Other equivalences are possible but would require argument permutation.
4001 * <p>
4002 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4003 * variable-arity method handle}, even if the original target method handle was.
4004 *
4005 * @param target the method handle to invoke after filtering the subsequence of arguments
4006 * @param pos the position of the first adapter argument to pass to the filter,
4007 * and/or the target argument which receives the result of the filter
4008 * @param filter method handle to call on the subsequence of arguments
4009 * @return method handle which incorporates the specified argument subsequence filtering logic
4010 * @throws NullPointerException if either argument is null
4011 * @throws IllegalArgumentException if the return type of {@code filter}
4012 * is non-void and is not the same as the {@code pos} argument of the target,
4013 * or if {@code pos} is not between 0 and the target's arity, inclusive,
4014 * or if the resulting method handle's type would have
4015 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4016 * @see MethodHandles#foldArguments
4017 * @see MethodHandles#filterArguments
4018 * @see MethodHandles#filterReturnValue
4019 */
4020 public static
4021 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
4022 MethodType newType = collectArgumentsChecks(target, pos, filter);
4023 MethodType collectorType = filter.type();
4024 BoundMethodHandle result = target.rebind();
4025 LambdaForm lform;
4026 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4027 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4028 if (lform != null) {
4029 return result.copyWith(newType, lform);
4030 }
4031 }
4032 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4033 return result.copyWithExtendL(newType, lform, filter);
4034 }
4035
4036 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4037 MethodType targetType = target.type();
4038 MethodType filterType = filter.type();
4039 Class<?> rtype = filterType.returnType();
4040 List<Class<?>> filterArgs = filterType.parameterList();
4041 if (rtype == void.class) {
4042 return targetType.insertParameterTypes(pos, filterArgs);
4043 }
4044 if (rtype != targetType.parameterType(pos)) {
4045 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4046 }
4047 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4048 }
4049
4050 /**
4051 * Adapts a target method handle by post-processing
4052 * its return value (if any) with a filter (another method handle).
4053 * The result of the filter is returned from the adapter.
4054 * <p>
4055 * If the target returns a value, the filter must accept that value as
4056 * its only argument.
4057 * If the target returns void, the filter must accept no arguments.
4058 * <p>
4059 * The return type of the filter
4060 * replaces the return type of the target
4061 * in the resulting adapted method handle.
4062 * The argument type of the filter (if any) must be identical to the
4063 * return type of the target.
4064 * <p><b>Example:</b>
4065 * <blockquote><pre>{@code
4066 import static java.lang.invoke.MethodHandles.*;
4067 import static java.lang.invoke.MethodType.*;
4068 ...
4069 MethodHandle cat = lookup().findVirtual(String.class,
4070 "concat", methodType(String.class, String.class));
4071 MethodHandle length = lookup().findVirtual(String.class,
4072 "length", methodType(int.class));
4073 System.out.println((String) cat.invokeExact("x", "y")); // xy
4074 MethodHandle f0 = filterReturnValue(cat, length);
4075 System.out.println((int) f0.invokeExact("x", "y")); // 2
4076 * }</pre></blockquote>
4077 * <p>Here is pseudocode for the resulting adapter. In the code,
4078 * {@code T}/{@code t} represent the result type and value of the
4079 * {@code target}; {@code V}, the result type of the {@code filter}; and
4080 * {@code A}/{@code a}, the types and values of the parameters and arguments
4081 * of the {@code target} as well as the resulting adapter.
4082 * <blockquote><pre>{@code
4083 * T target(A...);
4084 * V filter(T);
4085 * V adapter(A... a) {
4086 * T t = target(a...);
4087 * return filter(t);
4088 * }
4089 * // and if the target has a void return:
4090 * void target2(A...);
4091 * V filter2();
4092 * V adapter2(A... a) {
4093 * target2(a...);
4094 * return filter2();
4095 * }
4096 * // and if the filter has a void return:
4097 * T target3(A...);
4098 * void filter3(V);
4099 * void adapter3(A... a) {
4100 * T t = target3(a...);
4101 * filter3(t);
4102 * }
4103 * }</pre></blockquote>
4104 * <p>
4105 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4106 * variable-arity method handle}, even if the original target method handle was.
4107 * @param target the method handle to invoke before filtering the return value
4108 * @param filter method handle to call on the return value
4109 * @return method handle which incorporates the specified return value filtering logic
4110 * @throws NullPointerException if either argument is null
4111 * @throws IllegalArgumentException if the argument list of {@code filter}
4112 * does not match the return type of target as described above
4113 */
4114 public static
4115 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4116 MethodType targetType = target.type();
4117 MethodType filterType = filter.type();
4118 filterReturnValueChecks(targetType, filterType);
4119 BoundMethodHandle result = target.rebind();
4120 BasicType rtype = BasicType.basicType(filterType.returnType());
4121 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4122 MethodType newType = targetType.changeReturnType(filterType.returnType());
4123 result = result.copyWithExtendL(newType, lform, filter);
4124 return result;
4125 }
4126
4127 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4128 Class<?> rtype = targetType.returnType();
4129 int filterValues = filterType.parameterCount();
4130 if (filterValues == 0
4131 ? (rtype != void.class)
4132 : (rtype != filterType.parameterType(0) || filterValues != 1))
4133 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4134 }
4135
4136 /**
4137 * Adapts a target method handle by pre-processing
4138 * some of its arguments, and then calling the target with
4139 * the result of the pre-processing, inserted into the original
4140 * sequence of arguments.
4141 * <p>
4142 * The pre-processing is performed by {@code combiner}, a second method handle.
4143 * Of the arguments passed to the adapter, the first {@code N} arguments
4144 * are copied to the combiner, which is then called.
4145 * (Here, {@code N} is defined as the parameter count of the combiner.)
4146 * After this, control passes to the target, with any result
4147 * from the combiner inserted before the original {@code N} incoming
4148 * arguments.
4149 * <p>
4150 * If the combiner returns a value, the first parameter type of the target
4151 * must be identical with the return type of the combiner, and the next
4152 * {@code N} parameter types of the target must exactly match the parameters
4153 * of the combiner.
4154 * <p>
4155 * If the combiner has a void return, no result will be inserted,
4156 * and the first {@code N} parameter types of the target
4157 * must exactly match the parameters of the combiner.
4158 * <p>
4159 * The resulting adapter is the same type as the target, except that the
4160 * first parameter type is dropped,
4161 * if it corresponds to the result of the combiner.
4162 * <p>
4163 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4164 * that either the combiner or the target does not wish to receive.
4165 * If some of the incoming arguments are destined only for the combiner,
4166 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4167 * arguments will not need to be live on the stack on entry to the
4168 * target.)
4169 * <p><b>Example:</b>
4170 * <blockquote><pre>{@code
4171 import static java.lang.invoke.MethodHandles.*;
4172 import static java.lang.invoke.MethodType.*;
4173 ...
4174 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4175 "println", methodType(void.class, String.class))
4176 .bindTo(System.out);
4177 MethodHandle cat = lookup().findVirtual(String.class,
4178 "concat", methodType(String.class, String.class));
4179 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4180 MethodHandle catTrace = foldArguments(cat, trace);
4181 // also prints "boo":
4182 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4183 * }</pre></blockquote>
4184 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4185 * represents the result type of the {@code target} and resulting adapter.
4186 * {@code V}/{@code v} represent the type and value of the parameter and argument
4187 * of {@code target} that precedes the folding position; {@code V} also is
4188 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4189 * types and values of the {@code N} parameters and arguments at the folding
4190 * position. {@code B}/{@code b} represent the types and values of the
4191 * {@code target} parameters and arguments that follow the folded parameters
4192 * and arguments.
4193 * <blockquote><pre>{@code
4194 * // there are N arguments in A...
4195 * T target(V, A[N]..., B...);
4196 * V combiner(A...);
4197 * T adapter(A... a, B... b) {
4198 * V v = combiner(a...);
4199 * return target(v, a..., b...);
4200 * }
4201 * // and if the combiner has a void return:
4202 * T target2(A[N]..., B...);
4203 * void combiner2(A...);
4204 * T adapter2(A... a, B... b) {
4205 * combiner2(a...);
4206 * return target2(a..., b...);
4207 * }
4208 * }</pre></blockquote>
4209 * <p>
4210 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4211 * variable-arity method handle}, even if the original target method handle was.
4212 * @param target the method handle to invoke after arguments are combined
4213 * @param combiner method handle to call initially on the incoming arguments
4214 * @return method handle which incorporates the specified argument folding logic
4215 * @throws NullPointerException if either argument is null
4216 * @throws IllegalArgumentException if {@code combiner}'s return type
4217 * is non-void and not the same as the first argument type of
4218 * the target, or if the initial {@code N} argument types
4219 * of the target
4220 * (skipping one matching the {@code combiner}'s return type)
4221 * are not identical with the argument types of {@code combiner}
4222 */
4223 public static
4224 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4225 return foldArguments(target, 0, combiner);
4226 }
4227
4228 /**
4229 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4230 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4231 * before the folded arguments.
4232 * <p>
4233 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4234 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4235 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4236 * 0.
4237 *
4238 * @apiNote Example:
4239 * <blockquote><pre>{@code
4240 import static java.lang.invoke.MethodHandles.*;
4241 import static java.lang.invoke.MethodType.*;
4242 ...
4243 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4244 "println", methodType(void.class, String.class))
4245 .bindTo(System.out);
4246 MethodHandle cat = lookup().findVirtual(String.class,
4247 "concat", methodType(String.class, String.class));
4248 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4249 MethodHandle catTrace = foldArguments(cat, 1, trace);
4250 // also prints "jum":
4251 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4252 * }</pre></blockquote>
4253 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4254 * represents the result type of the {@code target} and resulting adapter.
4255 * {@code V}/{@code v} represent the type and value of the parameter and argument
4256 * of {@code target} that precedes the folding position; {@code V} also is
4257 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4258 * types and values of the {@code N} parameters and arguments at the folding
4259 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4260 * and values of the {@code target} parameters and arguments that precede and
4261 * follow the folded parameters and arguments starting at {@code pos},
4262 * respectively.
4263 * <blockquote><pre>{@code
4264 * // there are N arguments in A...
4265 * T target(Z..., V, A[N]..., B...);
4266 * V combiner(A...);
4267 * T adapter(Z... z, A... a, B... b) {
4268 * V v = combiner(a...);
4269 * return target(z..., v, a..., b...);
4270 * }
4271 * // and if the combiner has a void return:
4272 * T target2(Z..., A[N]..., B...);
4273 * void combiner2(A...);
4274 * T adapter2(Z... z, A... a, B... b) {
4275 * combiner2(a...);
4276 * return target2(z..., a..., b...);
4277 * }
4278 * }</pre></blockquote>
4279 * <p>
4280 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4281 * variable-arity method handle}, even if the original target method handle was.
4282 *
4283 * @param target the method handle to invoke after arguments are combined
4284 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4285 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4286 * @param combiner method handle to call initially on the incoming arguments
4287 * @return method handle which incorporates the specified argument folding logic
4288 * @throws NullPointerException if either argument is null
4289 * @throws IllegalArgumentException if either of the following two conditions holds:
4290 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4291 * {@code pos} of the target signature;
4292 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4293 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4294 *
4295 * @see #foldArguments(MethodHandle, MethodHandle)
4296 * @since 9
4297 */
4298 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4299 MethodType targetType = target.type();
4300 MethodType combinerType = combiner.type();
4301 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4302 BoundMethodHandle result = target.rebind();
4303 boolean dropResult = rtype == void.class;
4304 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4305 MethodType newType = targetType;
4306 if (!dropResult) {
4307 newType = newType.dropParameterTypes(pos, pos + 1);
4308 }
4309 result = result.copyWithExtendL(newType, lform, combiner);
4310 return result;
4311 }
4312
4313 /**
4314 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
4315 * added capability of selecting the arguments from the targets parameters
4316 * to call the combiner with. This allows us to avoid some simple cases of
4317 * permutations and padding the combiner with dropArguments to select the
4318 * right argument, which may ultimately produce fewer intermediaries.
4319 */
4320 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
4321 MethodType targetType = target.type();
4322 MethodType combinerType = combiner.type();
4323 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
4324 BoundMethodHandle result = target.rebind();
4325 boolean dropResult = rtype == void.class;
4326 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
4327 MethodType newType = targetType;
4328 if (!dropResult) {
4329 newType = newType.dropParameterTypes(pos, pos + 1);
4330 }
4331 result = result.copyWithExtendL(newType, lform, combiner);
4332 return result;
4333 }
4334
4335 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4336 int foldArgs = combinerType.parameterCount();
4337 Class<?> rtype = combinerType.returnType();
4338 int foldVals = rtype == void.class ? 0 : 1;
4339 int afterInsertPos = foldPos + foldVals;
4340 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4341 if (ok) {
4342 for (int i = 0; i < foldArgs; i++) {
4343 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4344 ok = false;
4345 break;
4346 }
4347 }
4348 }
4349 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4350 ok = false;
4351 if (!ok)
4352 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4353 return rtype;
4354 }
4355
4356 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
4357 int foldArgs = combinerType.parameterCount();
4358 if (argPos.length != foldArgs) {
4359 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4360 }
4361 Class<?> rtype = combinerType.returnType();
4362 int foldVals = rtype == void.class ? 0 : 1;
4363 boolean ok = true;
4364 for (int i = 0; i < foldArgs; i++) {
4365 int arg = argPos[i];
4366 if (arg < 0 || arg > targetType.parameterCount()) {
4367 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4368 }
4369 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4370 throw newIllegalArgumentException("target argument type at position " + arg
4371 + " must match combiner argument type at index " + i + ": " + targetType
4372 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4373 }
4374 }
4375 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
4376 ok = false;
4377 }
4378 if (!ok)
4379 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4380 return rtype;
4381 }
4382
4383 /**
4384 * Makes a method handle which adapts a target method handle,
4385 * by guarding it with a test, a boolean-valued method handle.
4386 * If the guard fails, a fallback handle is called instead.
4387 * All three method handles must have the same corresponding
4388 * argument and return types, except that the return type
4389 * of the test must be boolean, and the test is allowed
4390 * to have fewer arguments than the other two method handles.
4391 * <p>
4392 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4393 * represents the uniform result type of the three involved handles;
4394 * {@code A}/{@code a}, the types and values of the {@code target}
4395 * parameters and arguments that are consumed by the {@code test}; and
4396 * {@code B}/{@code b}, those types and values of the {@code target}
4397 * parameters and arguments that are not consumed by the {@code test}.
4398 * <blockquote><pre>{@code
4399 * boolean test(A...);
4400 * T target(A...,B...);
4401 * T fallback(A...,B...);
4402 * T adapter(A... a,B... b) {
4403 * if (test(a...))
4404 * return target(a..., b...);
4405 * else
4406 * return fallback(a..., b...);
4407 * }
4408 * }</pre></blockquote>
4409 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4410 * be modified by execution of the test, and so are passed unchanged
4411 * from the caller to the target or fallback as appropriate.
4412 * @param test method handle used for test, must return boolean
4413 * @param target method handle to call if test passes
4414 * @param fallback method handle to call if test fails
4415 * @return method handle which incorporates the specified if/then/else logic
4416 * @throws NullPointerException if any argument is null
4417 * @throws IllegalArgumentException if {@code test} does not return boolean,
4418 * or if all three method types do not match (with the return
4419 * type of {@code test} changed to match that of the target).
4420 */
4421 public static
4422 MethodHandle guardWithTest(MethodHandle test,
4423 MethodHandle target,
4424 MethodHandle fallback) {
4425 MethodType gtype = test.type();
4426 MethodType ttype = target.type();
4427 MethodType ftype = fallback.type();
4428 if (!ttype.equals(ftype))
4429 throw misMatchedTypes("target and fallback types", ttype, ftype);
4430 if (gtype.returnType() != boolean.class)
4431 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4432 List<Class<?>> targs = ttype.parameterList();
4433 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4434 if (test == null) {
4435 throw misMatchedTypes("target and test types", ttype, gtype);
4436 }
4437 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4438 }
4439
4440 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4441 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4442 }
4443
4444 /**
4445 * Makes a method handle which adapts a target method handle,
4446 * by running it inside an exception handler.
4447 * If the target returns normally, the adapter returns that value.
4448 * If an exception matching the specified type is thrown, the fallback
4449 * handle is called instead on the exception, plus the original arguments.
4450 * <p>
4451 * The target and handler must have the same corresponding
4452 * argument and return types, except that handler may omit trailing arguments
4453 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4454 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4455 * <p>
4456 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4457 * represents the return type of the {@code target} and {@code handler},
4458 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4459 * the types and values of arguments to the resulting handle consumed by
4460 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4461 * resulting handle discarded by {@code handler}.
4462 * <blockquote><pre>{@code
4463 * T target(A..., B...);
4464 * T handler(ExType, A...);
4465 * T adapter(A... a, B... b) {
4466 * try {
4467 * return target(a..., b...);
4468 * } catch (ExType ex) {
4469 * return handler(ex, a...);
4470 * }
4471 * }
4472 * }</pre></blockquote>
4473 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4474 * be modified by execution of the target, and so are passed unchanged
4475 * from the caller to the handler, if the handler is invoked.
4476 * <p>
4477 * The target and handler must return the same type, even if the handler
4478 * always throws. (This might happen, for instance, because the handler
4479 * is simulating a {@code finally} clause).
4480 * To create such a throwing handler, compose the handler creation logic
4481 * with {@link #throwException throwException},
4482 * in order to create a method handle of the correct return type.
4483 * @param target method handle to call
4484 * @param exType the type of exception which the handler will catch
4485 * @param handler method handle to call if a matching exception is thrown
4486 * @return method handle which incorporates the specified try/catch logic
4487 * @throws NullPointerException if any argument is null
4488 * @throws IllegalArgumentException if {@code handler} does not accept
4489 * the given exception type, or if the method handle types do
4490 * not match in their return types and their
4491 * corresponding parameters
4492 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4493 */
4494 public static
4495 MethodHandle catchException(MethodHandle target,
4496 Class<? extends Throwable> exType,
4497 MethodHandle handler) {
4498 MethodType ttype = target.type();
4499 MethodType htype = handler.type();
4500 if (!Throwable.class.isAssignableFrom(exType))
4501 throw new ClassCastException(exType.getName());
4502 if (htype.parameterCount() < 1 ||
4503 !htype.parameterType(0).isAssignableFrom(exType))
4504 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4505 if (htype.returnType() != ttype.returnType())
4506 throw misMatchedTypes("target and handler return types", ttype, htype);
4507 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4508 if (handler == null) {
4509 throw misMatchedTypes("target and handler types", ttype, htype);
4510 }
4511 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4512 }
4513
4514 /**
4515 * Produces a method handle which will throw exceptions of the given {@code exType}.
4516 * The method handle will accept a single argument of {@code exType},
4517 * and immediately throw it as an exception.
4518 * The method type will nominally specify a return of {@code returnType}.
4519 * The return type may be anything convenient: It doesn't matter to the
4520 * method handle's behavior, since it will never return normally.
4521 * @param returnType the return type of the desired method handle
4522 * @param exType the parameter type of the desired method handle
4523 * @return method handle which can throw the given exceptions
4524 * @throws NullPointerException if either argument is null
4525 */
4526 public static
4527 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4528 if (!Throwable.class.isAssignableFrom(exType))
4529 throw new ClassCastException(exType.getName());
4530 return MethodHandleImpl.throwException(methodType(returnType, exType));
4531 }
4532
4533 /**
4534 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4535 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4536 * delivers the loop's result, which is the return value of the resulting handle.
4537 * <p>
4538 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4539 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4540 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4541 * terms of method handles, each clause will specify up to four independent actions:<ul>
4542 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4543 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4544 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4545 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4546 * </ul>
4547 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4548 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4549 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4550 * <p>
4551 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4552 * this case. See below for a detailed description.
4553 * <p>
4554 * <em>Parameters optional everywhere:</em>
4555 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4556 * As an exception, the init functions cannot take any {@code v} parameters,
4557 * because those values are not yet computed when the init functions are executed.
4558 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4559 * In fact, any clause function may take no arguments at all.
4560 * <p>
4561 * <em>Loop parameters:</em>
4562 * A clause function may take all the iteration variable values it is entitled to, in which case
4563 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4564 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4565 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4566 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4567 * init function is automatically a loop parameter {@code a}.)
4568 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4569 * These loop parameters act as loop-invariant values visible across the whole loop.
4570 * <p>
4571 * <em>Parameters visible everywhere:</em>
4572 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4573 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4574 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4575 * Most clause functions will not need all of this information, but they will be formally connected to it
4576 * as if by {@link #dropArguments}.
4577 * <a id="astar"></a>
4578 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4579 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4580 * In that notation, the general form of an init function parameter list
4581 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4582 * <p>
4583 * <em>Checking clause structure:</em>
4584 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4585 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4586 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4587 * met by the inputs to the loop combinator.
4588 * <p>
4589 * <em>Effectively identical sequences:</em>
4590 * <a id="effid"></a>
4591 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4592 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4593 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4594 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4595 * that longest list.
4596 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4597 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4598 * <p>
4599 * <em>Step 0: Determine clause structure.</em><ol type="a">
4600 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4601 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4602 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4603 * four. Padding takes place by appending elements to the array.
4604 * <li>Clauses with all {@code null}s are disregarded.
4605 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4606 * </ol>
4607 * <p>
4608 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4609 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4610 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4611 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4612 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4613 * iteration variable type.
4614 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4615 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4616 * </ol>
4617 * <p>
4618 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4619 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4620 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4621 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4622 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4623 * (These types will be checked in step 2, along with all the clause function types.)
4624 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4625 * <li>All of the collected parameter lists must be effectively identical.
4626 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4627 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4628 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4629 * the "internal parameter list".
4630 * </ul>
4631 * <p>
4632 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4633 * <li>Examine fini function return types, disregarding omitted fini functions.
4634 * <li>If there are no fini functions, the loop return type is {@code void}.
4635 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4636 * type.
4637 * </ol>
4638 * <p>
4639 * <em>Step 1D: Check other types.</em><ol type="a">
4640 * <li>There must be at least one non-omitted pred function.
4641 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4642 * </ol>
4643 * <p>
4644 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4645 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4646 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4647 * (Note that their parameter lists are already effectively identical to this list.)
4648 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4649 * effectively identical to the internal parameter list {@code (V... A...)}.
4650 * </ol>
4651 * <p>
4652 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4653 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4654 * type.
4655 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4656 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4657 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4658 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4659 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4660 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4661 * loop return type.
4662 * </ol>
4663 * <p>
4664 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4665 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4666 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4667 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4668 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4669 * pad out the end of the list.
4670 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
4671 * </ol>
4672 * <p>
4673 * <em>Final observations.</em><ol type="a">
4674 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4675 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4676 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4677 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4678 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4679 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4680 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4681 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4682 * </ol>
4683 * <p>
4684 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4685 * <ul>
4686 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4687 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4688 * (Only one {@code Pn} has to be non-{@code null}.)
4689 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4690 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4691 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4692 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4693 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4694 * the resulting loop handle's parameter types {@code (A...)}.
4695 * </ul>
4696 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4697 * which is natural if most of the loop computation happens in the steps. For some loops,
4698 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4699 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4700 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4701 * where the init functions will need the extra parameters. For such reasons, the rules for
4702 * determining these parameters are as symmetric as possible, across all clause parts.
4703 * In general, the loop parameters function as common invariant values across the whole
4704 * loop, while the iteration variables function as common variant values, or (if there is
4705 * no step function) as internal loop invariant temporaries.
4706 * <p>
4707 * <em>Loop execution.</em><ol type="a">
4708 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4709 * every clause function. These locals are loop invariant.
4710 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4711 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4712 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4713 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4714 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4715 * (in argument order).
4716 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4717 * returns {@code false}.
4718 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4719 * sequence {@code (v...)} of loop variables.
4720 * The updated value is immediately visible to all subsequent function calls.
4721 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4722 * (of type {@code R}) is returned from the loop as a whole.
4723 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4724 * except by throwing an exception.
4725 * </ol>
4726 * <p>
4727 * <em>Usage tips.</em>
4728 * <ul>
4729 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4730 * sometimes a step function only needs to observe the current value of its own variable.
4731 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4732 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4733 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4734 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4735 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4736 * <li>If some of the clause functions are virtual methods on an instance, the instance
4737 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4738 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4739 * will be the first iteration variable value, and it will be easy to use virtual
4740 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4741 * </ul>
4742 * <p>
4743 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4744 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4745 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4746 * <blockquote><pre>{@code
4747 * V... init...(A...);
4748 * boolean pred...(V..., A...);
4749 * V... step...(V..., A...);
4750 * R fini...(V..., A...);
4751 * R loop(A... a) {
4752 * V... v... = init...(a...);
4753 * for (;;) {
4754 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4755 * v = s(v..., a...);
4756 * if (!p(v..., a...)) {
4757 * return f(v..., a...);
4758 * }
4759 * }
4760 * }
4761 * }
4762 * }</pre></blockquote>
4763 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4764 * to their full length, even though individual clause functions may neglect to take them all.
4765 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
4766 *
4767 * @apiNote Example:
4768 * <blockquote><pre>{@code
4769 * // iterative implementation of the factorial function as a loop handle
4770 * static int one(int k) { return 1; }
4771 * static int inc(int i, int acc, int k) { return i + 1; }
4772 * static int mult(int i, int acc, int k) { return i * acc; }
4773 * static boolean pred(int i, int acc, int k) { return i < k; }
4774 * static int fin(int i, int acc, int k) { return acc; }
4775 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4776 * // null initializer for counter, should initialize to 0
4777 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4778 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4779 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4780 * assertEquals(120, loop.invoke(5));
4781 * }</pre></blockquote>
4782 * The same example, dropping arguments and using combinators:
4783 * <blockquote><pre>{@code
4784 * // simplified implementation of the factorial function as a loop handle
4785 * static int inc(int i) { return i + 1; } // drop acc, k
4786 * static int mult(int i, int acc) { return i * acc; } //drop k
4787 * static boolean cmp(int i, int k) { return i < k; }
4788 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4789 * // null initializer for counter, should initialize to 0
4790 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4791 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4792 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4793 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4794 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4795 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4796 * assertEquals(720, loop.invoke(6));
4797 * }</pre></blockquote>
4798 * A similar example, using a helper object to hold a loop parameter:
4799 * <blockquote><pre>{@code
4800 * // instance-based implementation of the factorial function as a loop handle
4801 * static class FacLoop {
4802 * final int k;
4803 * FacLoop(int k) { this.k = k; }
4804 * int inc(int i) { return i + 1; }
4805 * int mult(int i, int acc) { return i * acc; }
4806 * boolean pred(int i) { return i < k; }
4807 * int fin(int i, int acc) { return acc; }
4808 * }
4809 * // assume MH_FacLoop is a handle to the constructor
4810 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4811 * // null initializer for counter, should initialize to 0
4812 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4813 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4814 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4815 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4816 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4817 * assertEquals(5040, loop.invoke(7));
4818 * }</pre></blockquote>
4819 *
4820 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4821 *
4822 * @return a method handle embodying the looping behavior as defined by the arguments.
4823 *
4824 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4825 *
4826 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4827 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4828 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4829 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4830 * @since 9
4831 */
4832 public static MethodHandle loop(MethodHandle[]... clauses) {
4833 // Step 0: determine clause structure.
4834 loopChecks0(clauses);
4835
4836 List<MethodHandle> init = new ArrayList<>();
4837 List<MethodHandle> step = new ArrayList<>();
4838 List<MethodHandle> pred = new ArrayList<>();
4839 List<MethodHandle> fini = new ArrayList<>();
4840
4841 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4842 init.add(clause[0]); // all clauses have at least length 1
4843 step.add(clause.length <= 1 ? null : clause[1]);
4844 pred.add(clause.length <= 2 ? null : clause[2]);
4845 fini.add(clause.length <= 3 ? null : clause[3]);
4846 });
4847
4848 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4849 final int nclauses = init.size();
4850
4851 // Step 1A: determine iteration variables (V...).
4852 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4853 for (int i = 0; i < nclauses; ++i) {
4854 MethodHandle in = init.get(i);
4855 MethodHandle st = step.get(i);
4856 if (in == null && st == null) {
4857 iterationVariableTypes.add(void.class);
4858 } else if (in != null && st != null) {
4859 loopChecks1a(i, in, st);
4860 iterationVariableTypes.add(in.type().returnType());
4861 } else {
4862 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4863 }
4864 }
4865 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4866 collect(Collectors.toList());
4867
4868 // Step 1B: determine loop parameters (A...).
4869 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4870 loopChecks1b(init, commonSuffix);
4871
4872 // Step 1C: determine loop return type.
4873 // Step 1D: check other types.
4874 // local variable required here; see JDK-8223553
4875 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
4876 .map(MethodType::returnType);
4877 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
4878 loopChecks1cd(pred, fini, loopReturnType);
4879
4880 // Step 2: determine parameter lists.
4881 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4882 commonParameterSequence.addAll(commonSuffix);
4883 loopChecks2(step, pred, fini, commonParameterSequence);
4884
4885 // Step 3: fill in omitted functions.
4886 for (int i = 0; i < nclauses; ++i) {
4887 Class<?> t = iterationVariableTypes.get(i);
4888 if (init.get(i) == null) {
4889 init.set(i, empty(methodType(t, commonSuffix)));
4890 }
4891 if (step.get(i) == null) {
4892 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4893 }
4894 if (pred.get(i) == null) {
4895 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4896 }
4897 if (fini.get(i) == null) {
4898 fini.set(i, empty(methodType(t, commonParameterSequence)));
4899 }
4900 }
4901
4902 // Step 4: fill in missing parameter types.
4903 // Also convert all handles to fixed-arity handles.
4904 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
4905 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
4906 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
4907 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
4908
4909 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4910 allMatch(pl -> pl.equals(commonSuffix));
4911 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4912 allMatch(pl -> pl.equals(commonParameterSequence));
4913
4914 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4915 }
4916
4917 private static void loopChecks0(MethodHandle[][] clauses) {
4918 if (clauses == null || clauses.length == 0) {
4919 throw newIllegalArgumentException("null or no clauses passed");
4920 }
4921 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4922 throw newIllegalArgumentException("null clauses are not allowed");
4923 }
4924 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4925 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4926 }
4927 }
4928
4929 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
4930 if (in.type().returnType() != st.type().returnType()) {
4931 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4932 st.type().returnType());
4933 }
4934 }
4935
4936 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
4937 final List<Class<?>> empty = List.of();
4938 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
4939 // take only those that can contribute to a common suffix because they are longer than the prefix
4940 map(MethodHandle::type).
4941 filter(t -> t.parameterCount() > skipSize).
4942 map(MethodType::parameterList).
4943 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4944 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
4945 }
4946
4947 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
4948 final List<Class<?>> empty = List.of();
4949 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4950 }
4951
4952 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4953 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
4954 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
4955 return longestParameterList(Arrays.asList(longest1, longest2));
4956 }
4957
4958 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4959 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
4960 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
4961 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4962 " (common suffix: " + commonSuffix + ")");
4963 }
4964 }
4965
4966 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4967 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4968 anyMatch(t -> t != loopReturnType)) {
4969 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4970 loopReturnType + ")");
4971 }
4972
4973 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4974 throw newIllegalArgumentException("no predicate found", pred);
4975 }
4976 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4977 anyMatch(t -> t != boolean.class)) {
4978 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4979 }
4980 }
4981
4982 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4983 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4984 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
4985 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4986 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4987 }
4988 }
4989
4990 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4991 return hs.stream().map(h -> {
4992 int pc = h.type().parameterCount();
4993 int tpsize = targetParams.size();
4994 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
4995 }).collect(Collectors.toList());
4996 }
4997
4998 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
4999 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
5000 }
5001
5002 /**
5003 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
5004 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5005 * <p>
5006 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5007 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
5008 * evaluates to {@code true}).
5009 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
5010 * <p>
5011 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5012 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5013 * and updated with the value returned from its invocation. The result of loop execution will be
5014 * the final value of the additional loop-local variable (if present).
5015 * <p>
5016 * The following rules hold for these argument handles:<ul>
5017 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5018 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5019 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5020 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5021 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5022 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5023 * It will constrain the parameter lists of the other loop parts.
5024 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5025 * list {@code (A...)} is called the <em>external parameter list</em>.
5026 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5027 * additional state variable of the loop.
5028 * The body must both accept and return a value of this type {@code V}.
5029 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5030 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5031 * <a href="MethodHandles.html#effid">effectively identical</a>
5032 * to the external parameter list {@code (A...)}.
5033 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5034 * {@linkplain #empty default value}.
5035 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5036 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5037 * effectively identical to the internal parameter list.
5038 * </ul>
5039 * <p>
5040 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5041 * <li>The loop handle's result type is the result type {@code V} of the body.
5042 * <li>The loop handle's parameter types are the types {@code (A...)},
5043 * from the external parameter list.
5044 * </ul>
5045 * <p>
5046 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5047 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5048 * passed to the loop.
5049 * <blockquote><pre>{@code
5050 * V init(A...);
5051 * boolean pred(V, A...);
5052 * V body(V, A...);
5053 * V whileLoop(A... a...) {
5054 * V v = init(a...);
5055 * while (pred(v, a...)) {
5056 * v = body(v, a...);
5057 * }
5058 * return v;
5059 * }
5060 * }</pre></blockquote>
5061 *
5062 * @apiNote Example:
5063 * <blockquote><pre>{@code
5064 * // implement the zip function for lists as a loop handle
5065 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5066 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5067 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5068 * zip.add(a.next());
5069 * zip.add(b.next());
5070 * return zip;
5071 * }
5072 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5073 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5074 * List<String> a = Arrays.asList("a", "b", "c", "d");
5075 * List<String> b = Arrays.asList("e", "f", "g", "h");
5076 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5077 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5078 * }</pre></blockquote>
5079 *
5080 *
5081 * @apiNote The implementation of this method can be expressed as follows:
5082 * <blockquote><pre>{@code
5083 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5084 * MethodHandle fini = (body.type().returnType() == void.class
5085 * ? null : identity(body.type().returnType()));
5086 * MethodHandle[]
5087 * checkExit = { null, null, pred, fini },
5088 * varBody = { init, body };
5089 * return loop(checkExit, varBody);
5090 * }
5091 * }</pre></blockquote>
5092 *
5093 * @param init optional initializer, providing the initial value of the loop variable.
5094 * May be {@code null}, implying a default initial value. See above for other constraints.
5095 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5096 * above for other constraints.
5097 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5098 * See above for other constraints.
5099 *
5100 * @return a method handle implementing the {@code while} loop as described by the arguments.
5101 * @throws IllegalArgumentException if the rules for the arguments are violated.
5102 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5103 *
5104 * @see #loop(MethodHandle[][])
5105 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5106 * @since 9
5107 */
5108 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5109 whileLoopChecks(init, pred, body);
5110 MethodHandle fini = identityOrVoid(body.type().returnType());
5111 MethodHandle[] checkExit = { null, null, pred, fini };
5112 MethodHandle[] varBody = { init, body };
5113 return loop(checkExit, varBody);
5114 }
5115
5116 /**
5117 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5118 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5119 * <p>
5120 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5121 * method will, in each iteration, first execute its body and then evaluate the predicate.
5122 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5123 * <p>
5124 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5125 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5126 * and updated with the value returned from its invocation. The result of loop execution will be
5127 * the final value of the additional loop-local variable (if present).
5128 * <p>
5129 * The following rules hold for these argument handles:<ul>
5130 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5131 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5132 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5133 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5134 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5135 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5136 * It will constrain the parameter lists of the other loop parts.
5137 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5138 * list {@code (A...)} is called the <em>external parameter list</em>.
5139 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5140 * additional state variable of the loop.
5141 * The body must both accept and return a value of this type {@code V}.
5142 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5143 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5144 * <a href="MethodHandles.html#effid">effectively identical</a>
5145 * to the external parameter list {@code (A...)}.
5146 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5147 * {@linkplain #empty default value}.
5148 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5149 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5150 * effectively identical to the internal parameter list.
5151 * </ul>
5152 * <p>
5153 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5154 * <li>The loop handle's result type is the result type {@code V} of the body.
5155 * <li>The loop handle's parameter types are the types {@code (A...)},
5156 * from the external parameter list.
5157 * </ul>
5158 * <p>
5159 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5160 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5161 * passed to the loop.
5162 * <blockquote><pre>{@code
5163 * V init(A...);
5164 * boolean pred(V, A...);
5165 * V body(V, A...);
5166 * V doWhileLoop(A... a...) {
5167 * V v = init(a...);
5168 * do {
5169 * v = body(v, a...);
5170 * } while (pred(v, a...));
5171 * return v;
5172 * }
5173 * }</pre></blockquote>
5174 *
5175 * @apiNote Example:
5176 * <blockquote><pre>{@code
5177 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5178 * static int zero(int limit) { return 0; }
5179 * static int step(int i, int limit) { return i + 1; }
5180 * static boolean pred(int i, int limit) { return i < limit; }
5181 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5182 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5183 * assertEquals(23, loop.invoke(23));
5184 * }</pre></blockquote>
5185 *
5186 *
5187 * @apiNote The implementation of this method can be expressed as follows:
5188 * <blockquote><pre>{@code
5189 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5190 * MethodHandle fini = (body.type().returnType() == void.class
5191 * ? null : identity(body.type().returnType()));
5192 * MethodHandle[] clause = { init, body, pred, fini };
5193 * return loop(clause);
5194 * }
5195 * }</pre></blockquote>
5196 *
5197 * @param init optional initializer, providing the initial value of the loop variable.
5198 * May be {@code null}, implying a default initial value. See above for other constraints.
5199 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5200 * See above for other constraints.
5201 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5202 * above for other constraints.
5203 *
5204 * @return a method handle implementing the {@code while} loop as described by the arguments.
5205 * @throws IllegalArgumentException if the rules for the arguments are violated.
5206 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5207 *
5208 * @see #loop(MethodHandle[][])
5209 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5210 * @since 9
5211 */
5212 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5213 whileLoopChecks(init, pred, body);
5214 MethodHandle fini = identityOrVoid(body.type().returnType());
5215 MethodHandle[] clause = {init, body, pred, fini };
5216 return loop(clause);
5217 }
5218
5219 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5220 Objects.requireNonNull(pred);
5221 Objects.requireNonNull(body);
5222 MethodType bodyType = body.type();
5223 Class<?> returnType = bodyType.returnType();
5224 List<Class<?>> innerList = bodyType.parameterList();
5225 List<Class<?>> outerList = innerList;
5226 if (returnType == void.class) {
5227 // OK
5228 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5229 // leading V argument missing => error
5230 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5231 throw misMatchedTypes("body function", bodyType, expected);
5232 } else {
5233 outerList = innerList.subList(1, innerList.size());
5234 }
5235 MethodType predType = pred.type();
5236 if (predType.returnType() != boolean.class ||
5237 !predType.effectivelyIdenticalParameters(0, innerList)) {
5238 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5239 }
5240 if (init != null) {
5241 MethodType initType = init.type();
5242 if (initType.returnType() != returnType ||
5243 !initType.effectivelyIdenticalParameters(0, outerList)) {
5244 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5245 }
5246 }
5247 }
5248
5249 /**
5250 * Constructs a loop that runs a given number of iterations.
5251 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5252 * <p>
5253 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5254 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5255 * It will be initialized to 0 and incremented by 1 in each iteration.
5256 * <p>
5257 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5258 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5259 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5260 * <p>
5261 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5262 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5263 * iteration variable.
5264 * The result of the loop handle execution will be the final {@code V} value of that variable
5265 * (or {@code void} if there is no {@code V} variable).
5266 * <p>
5267 * The following rules hold for the argument handles:<ul>
5268 * <li>The {@code iterations} handle must not be {@code null}, and must return
5269 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5270 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5271 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5272 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5273 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5274 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5275 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5276 * of types called the <em>internal parameter list</em>.
5277 * It will constrain the parameter lists of the other loop parts.
5278 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5279 * with no additional {@code A} types, then the internal parameter list is extended by
5280 * the argument types {@code A...} of the {@code iterations} handle.
5281 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5282 * list {@code (A...)} is called the <em>external parameter list</em>.
5283 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5284 * additional state variable of the loop.
5285 * The body must both accept a leading parameter and return a value of this type {@code V}.
5286 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5287 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5288 * <a href="MethodHandles.html#effid">effectively identical</a>
5289 * to the external parameter list {@code (A...)}.
5290 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5291 * {@linkplain #empty default value}.
5292 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5293 * effectively identical to the external parameter list {@code (A...)}.
5294 * </ul>
5295 * <p>
5296 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5297 * <li>The loop handle's result type is the result type {@code V} of the body.
5298 * <li>The loop handle's parameter types are the types {@code (A...)},
5299 * from the external parameter list.
5300 * </ul>
5301 * <p>
5302 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5303 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5304 * arguments passed to the loop.
5305 * <blockquote><pre>{@code
5306 * int iterations(A...);
5307 * V init(A...);
5308 * V body(V, int, A...);
5309 * V countedLoop(A... a...) {
5310 * int end = iterations(a...);
5311 * V v = init(a...);
5312 * for (int i = 0; i < end; ++i) {
5313 * v = body(v, i, a...);
5314 * }
5315 * return v;
5316 * }
5317 * }</pre></blockquote>
5318 *
5319 * @apiNote Example with a fully conformant body method:
5320 * <blockquote><pre>{@code
5321 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5322 * // => a variation on a well known theme
5323 * static String step(String v, int counter, String init) { return "na " + v; }
5324 * // assume MH_step is a handle to the method above
5325 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5326 * MethodHandle start = MethodHandles.identity(String.class);
5327 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5328 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5329 * }</pre></blockquote>
5330 *
5331 * @apiNote Example with the simplest possible body method type,
5332 * and passing the number of iterations to the loop invocation:
5333 * <blockquote><pre>{@code
5334 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5335 * // => a variation on a well known theme
5336 * static String step(String v, int counter ) { return "na " + v; }
5337 * // assume MH_step is a handle to the method above
5338 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5339 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5340 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5341 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5342 * }</pre></blockquote>
5343 *
5344 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5345 * as loop parameters:
5346 * <blockquote><pre>{@code
5347 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5348 * // => a variation on a well known theme
5349 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5350 * // assume MH_step is a handle to the method above
5351 * MethodHandle count = MethodHandles.identity(int.class);
5352 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5353 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5354 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5355 * }</pre></blockquote>
5356 *
5357 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5358 * to enforce a loop type:
5359 * <blockquote><pre>{@code
5360 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5361 * // => a variation on a well known theme
5362 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5363 * // assume MH_step is a handle to the method above
5364 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5365 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5366 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5367 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5368 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5369 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5370 * }</pre></blockquote>
5371 *
5372 * @apiNote The implementation of this method can be expressed as follows:
5373 * <blockquote><pre>{@code
5374 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5375 * return countedLoop(empty(iterations.type()), iterations, init, body);
5376 * }
5377 * }</pre></blockquote>
5378 *
5379 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5380 * result type must be {@code int}. See above for other constraints.
5381 * @param init optional initializer, providing the initial value of the loop variable.
5382 * May be {@code null}, implying a default initial value. See above for other constraints.
5383 * @param body body of the loop, which may not be {@code null}.
5384 * It controls the loop parameters and result type in the standard case (see above for details).
5385 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5386 * and may accept any number of additional types.
5387 * See above for other constraints.
5388 *
5389 * @return a method handle representing the loop.
5390 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5391 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5392 *
5393 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5394 * @since 9
5395 */
5396 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5397 return countedLoop(empty(iterations.type()), iterations, init, body);
5398 }
5399
5400 /**
5401 * Constructs a loop that counts over a range of numbers.
5402 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5403 * <p>
5404 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5405 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5406 * values of the loop counter.
5407 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5408 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5409 * <p>
5410 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5411 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5412 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5413 * <p>
5414 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5415 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5416 * iteration variable.
5417 * The result of the loop handle execution will be the final {@code V} value of that variable
5418 * (or {@code void} if there is no {@code V} variable).
5419 * <p>
5420 * The following rules hold for the argument handles:<ul>
5421 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5422 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5423 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5424 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5425 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5426 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5427 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5428 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5429 * of types called the <em>internal parameter list</em>.
5430 * It will constrain the parameter lists of the other loop parts.
5431 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5432 * with no additional {@code A} types, then the internal parameter list is extended by
5433 * the argument types {@code A...} of the {@code end} handle.
5434 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5435 * list {@code (A...)} is called the <em>external parameter list</em>.
5436 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5437 * additional state variable of the loop.
5438 * The body must both accept a leading parameter and return a value of this type {@code V}.
5439 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5440 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5441 * <a href="MethodHandles.html#effid">effectively identical</a>
5442 * to the external parameter list {@code (A...)}.
5443 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5444 * {@linkplain #empty default value}.
5445 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5446 * effectively identical to the external parameter list {@code (A...)}.
5447 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5448 * to the external parameter list.
5449 * </ul>
5450 * <p>
5451 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5452 * <li>The loop handle's result type is the result type {@code V} of the body.
5453 * <li>The loop handle's parameter types are the types {@code (A...)},
5454 * from the external parameter list.
5455 * </ul>
5456 * <p>
5457 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5458 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5459 * arguments passed to the loop.
5460 * <blockquote><pre>{@code
5461 * int start(A...);
5462 * int end(A...);
5463 * V init(A...);
5464 * V body(V, int, A...);
5465 * V countedLoop(A... a...) {
5466 * int e = end(a...);
5467 * int s = start(a...);
5468 * V v = init(a...);
5469 * for (int i = s; i < e; ++i) {
5470 * v = body(v, i, a...);
5471 * }
5472 * return v;
5473 * }
5474 * }</pre></blockquote>
5475 *
5476 * @apiNote The implementation of this method can be expressed as follows:
5477 * <blockquote><pre>{@code
5478 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5479 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5480 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5481 * // the following semantics:
5482 * // MH_increment: (int limit, int counter) -> counter + 1
5483 * // MH_predicate: (int limit, int counter) -> counter < limit
5484 * Class<?> counterType = start.type().returnType(); // int
5485 * Class<?> returnType = body.type().returnType();
5486 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5487 * if (returnType != void.class) { // ignore the V variable
5488 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5489 * pred = dropArguments(pred, 1, returnType); // ditto
5490 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5491 * }
5492 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5493 * MethodHandle[]
5494 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5495 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5496 * indexVar = { start, incr }; // i = start(); i = i + 1
5497 * return loop(loopLimit, bodyClause, indexVar);
5498 * }
5499 * }</pre></blockquote>
5500 *
5501 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5502 * See above for other constraints.
5503 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5504 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5505 * @param init optional initializer, providing the initial value of the loop variable.
5506 * May be {@code null}, implying a default initial value. See above for other constraints.
5507 * @param body body of the loop, which may not be {@code null}.
5508 * It controls the loop parameters and result type in the standard case (see above for details).
5509 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5510 * and may accept any number of additional types.
5511 * See above for other constraints.
5512 *
5513 * @return a method handle representing the loop.
5514 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5515 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5516 *
5517 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5518 * @since 9
5519 */
5520 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5521 countedLoopChecks(start, end, init, body);
5522 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5523 Class<?> limitType = end.type().returnType(); // yes, int again
5524 Class<?> returnType = body.type().returnType();
5525 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5526 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5527 MethodHandle retv = null;
5528 if (returnType != void.class) {
5529 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5530 pred = dropArguments(pred, 1, returnType); // ditto
5531 retv = dropArguments(identity(returnType), 0, counterType);
5532 }
5533 body = dropArguments(body, 0, counterType); // ignore the limit variable
5534 MethodHandle[]
5535 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5536 bodyClause = { init, body }, // v = init(); v = body(v, i)
5537 indexVar = { start, incr }; // i = start(); i = i + 1
5538 return loop(loopLimit, bodyClause, indexVar);
5539 }
5540
5541 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5542 Objects.requireNonNull(start);
5543 Objects.requireNonNull(end);
5544 Objects.requireNonNull(body);
5545 Class<?> counterType = start.type().returnType();
5546 if (counterType != int.class) {
5547 MethodType expected = start.type().changeReturnType(int.class);
5548 throw misMatchedTypes("start function", start.type(), expected);
5549 } else if (end.type().returnType() != counterType) {
5550 MethodType expected = end.type().changeReturnType(counterType);
5551 throw misMatchedTypes("end function", end.type(), expected);
5552 }
5553 MethodType bodyType = body.type();
5554 Class<?> returnType = bodyType.returnType();
5555 List<Class<?>> innerList = bodyType.parameterList();
5556 // strip leading V value if present
5557 int vsize = (returnType == void.class ? 0 : 1);
5558 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5559 // argument list has no "V" => error
5560 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5561 throw misMatchedTypes("body function", bodyType, expected);
5562 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5563 // missing I type => error
5564 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5565 throw misMatchedTypes("body function", bodyType, expected);
5566 }
5567 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5568 if (outerList.isEmpty()) {
5569 // special case; take lists from end handle
5570 outerList = end.type().parameterList();
5571 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5572 }
5573 MethodType expected = methodType(counterType, outerList);
5574 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5575 throw misMatchedTypes("start parameter types", start.type(), expected);
5576 }
5577 if (end.type() != start.type() &&
5578 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5579 throw misMatchedTypes("end parameter types", end.type(), expected);
5580 }
5581 if (init != null) {
5582 MethodType initType = init.type();
5583 if (initType.returnType() != returnType ||
5584 !initType.effectivelyIdenticalParameters(0, outerList)) {
5585 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5586 }
5587 }
5588 }
5589
5590 /**
5591 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5592 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5593 * <p>
5594 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5595 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5596 * <p>
5597 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5598 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5599 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5600 * <p>
5601 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5602 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5603 * iteration variable.
5604 * The result of the loop handle execution will be the final {@code V} value of that variable
5605 * (or {@code void} if there is no {@code V} variable).
5606 * <p>
5607 * The following rules hold for the argument handles:<ul>
5608 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5609 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5610 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5611 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5612 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5613 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5614 * of types called the <em>internal parameter list</em>.
5615 * It will constrain the parameter lists of the other loop parts.
5616 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5617 * with no additional {@code A} types, then the internal parameter list is extended by
5618 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5619 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5620 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5621 * list {@code (A...)} is called the <em>external parameter list</em>.
5622 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5623 * additional state variable of the loop.
5624 * The body must both accept a leading parameter and return a value of this type {@code V}.
5625 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5626 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5627 * <a href="MethodHandles.html#effid">effectively identical</a>
5628 * to the external parameter list {@code (A...)}.
5629 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5630 * {@linkplain #empty default value}.
5631 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5632 * type {@code java.util.Iterator} or a subtype thereof.
5633 * The iterator it produces when the loop is executed will be assumed
5634 * to yield values which can be converted to type {@code T}.
5635 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5636 * effectively identical to the external parameter list {@code (A...)}.
5637 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5638 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5639 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5640 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5641 * the {@link MethodHandle#asType asType} conversion method.
5642 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5643 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5644 * </ul>
5645 * <p>
5646 * The type {@code T} may be either a primitive or reference.
5647 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5648 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5649 * as if by the {@link MethodHandle#asType asType} conversion method.
5650 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5651 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5652 * <p>
5653 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5654 * <li>The loop handle's result type is the result type {@code V} of the body.
5655 * <li>The loop handle's parameter types are the types {@code (A...)},
5656 * from the external parameter list.
5657 * </ul>
5658 * <p>
5659 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5660 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5661 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5662 * <blockquote><pre>{@code
5663 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5664 * V init(A...);
5665 * V body(V,T,A...);
5666 * V iteratedLoop(A... a...) {
5667 * Iterator<T> it = iterator(a...);
5668 * V v = init(a...);
5669 * while (it.hasNext()) {
5670 * T t = it.next();
5671 * v = body(v, t, a...);
5672 * }
5673 * return v;
5674 * }
5675 * }</pre></blockquote>
5676 *
5677 * @apiNote Example:
5678 * <blockquote><pre>{@code
5679 * // get an iterator from a list
5680 * static List<String> reverseStep(List<String> r, String e) {
5681 * r.add(0, e);
5682 * return r;
5683 * }
5684 * static List<String> newArrayList() { return new ArrayList<>(); }
5685 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5686 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5687 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5688 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5689 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5690 * }</pre></blockquote>
5691 *
5692 * @apiNote The implementation of this method can be expressed approximately as follows:
5693 * <blockquote><pre>{@code
5694 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5695 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5696 * Class<?> returnType = body.type().returnType();
5697 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5698 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5699 * MethodHandle retv = null, step = body, startIter = iterator;
5700 * if (returnType != void.class) {
5701 * // the simple thing first: in (I V A...), drop the I to get V
5702 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5703 * // body type signature (V T A...), internal loop types (I V A...)
5704 * step = swapArguments(body, 0, 1); // swap V <-> T
5705 * }
5706 * if (startIter == null) startIter = MH_getIter;
5707 * MethodHandle[]
5708 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5709 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5710 * return loop(iterVar, bodyClause);
5711 * }
5712 * }</pre></blockquote>
5713 *
5714 * @param iterator an optional handle to return the iterator to start the loop.
5715 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5716 * See above for other constraints.
5717 * @param init optional initializer, providing the initial value of the loop variable.
5718 * May be {@code null}, implying a default initial value. See above for other constraints.
5719 * @param body body of the loop, which may not be {@code null}.
5720 * It controls the loop parameters and result type in the standard case (see above for details).
5721 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5722 * and may accept any number of additional types.
5723 * See above for other constraints.
5724 *
5725 * @return a method handle embodying the iteration loop functionality.
5726 * @throws NullPointerException if the {@code body} handle is {@code null}.
5727 * @throws IllegalArgumentException if any argument violates the above requirements.
5728 *
5729 * @since 9
5730 */
5731 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5732 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5733 Class<?> returnType = body.type().returnType();
5734 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5735 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5736 MethodHandle startIter;
5737 MethodHandle nextVal;
5738 {
5739 MethodType iteratorType;
5740 if (iterator == null) {
5741 // derive argument type from body, if available, else use Iterable
5742 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5743 iteratorType = startIter.type().changeParameterType(0, iterableType);
5744 } else {
5745 // force return type to the internal iterator class
5746 iteratorType = iterator.type().changeReturnType(Iterator.class);
5747 startIter = iterator;
5748 }
5749 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5750 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5751
5752 // perform the asType transforms under an exception transformer, as per spec.:
5753 try {
5754 startIter = startIter.asType(iteratorType);
5755 nextVal = nextRaw.asType(nextValType);
5756 } catch (WrongMethodTypeException ex) {
5757 throw new IllegalArgumentException(ex);
5758 }
5759 }
5760
5761 MethodHandle retv = null, step = body;
5762 if (returnType != void.class) {
5763 // the simple thing first: in (I V A...), drop the I to get V
5764 retv = dropArguments(identity(returnType), 0, Iterator.class);
5765 // body type signature (V T A...), internal loop types (I V A...)
5766 step = swapArguments(body, 0, 1); // swap V <-> T
5767 }
5768
5769 MethodHandle[]
5770 iterVar = { startIter, null, hasNext, retv },
5771 bodyClause = { init, filterArgument(step, 0, nextVal) };
5772 return loop(iterVar, bodyClause);
5773 }
5774
5775 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5776 Objects.requireNonNull(body);
5777 MethodType bodyType = body.type();
5778 Class<?> returnType = bodyType.returnType();
5779 List<Class<?>> internalParamList = bodyType.parameterList();
5780 // strip leading V value if present
5781 int vsize = (returnType == void.class ? 0 : 1);
5782 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5783 // argument list has no "V" => error
5784 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5785 throw misMatchedTypes("body function", bodyType, expected);
5786 } else if (internalParamList.size() <= vsize) {
5787 // missing T type => error
5788 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5789 throw misMatchedTypes("body function", bodyType, expected);
5790 }
5791 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5792 Class<?> iterableType = null;
5793 if (iterator != null) {
5794 // special case; if the body handle only declares V and T then
5795 // the external parameter list is obtained from iterator handle
5796 if (externalParamList.isEmpty()) {
5797 externalParamList = iterator.type().parameterList();
5798 }
5799 MethodType itype = iterator.type();
5800 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5801 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5802 }
5803 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5804 MethodType expected = methodType(itype.returnType(), externalParamList);
5805 throw misMatchedTypes("iterator parameters", itype, expected);
5806 }
5807 } else {
5808 if (externalParamList.isEmpty()) {
5809 // special case; if the iterator handle is null and the body handle
5810 // only declares V and T then the external parameter list consists
5811 // of Iterable
5812 externalParamList = Arrays.asList(Iterable.class);
5813 iterableType = Iterable.class;
5814 } else {
5815 // special case; if the iterator handle is null and the external
5816 // parameter list is not empty then the first parameter must be
5817 // assignable to Iterable
5818 iterableType = externalParamList.get(0);
5819 if (!Iterable.class.isAssignableFrom(iterableType)) {
5820 throw newIllegalArgumentException(
5821 "inferred first loop argument must inherit from Iterable: " + iterableType);
5822 }
5823 }
5824 }
5825 if (init != null) {
5826 MethodType initType = init.type();
5827 if (initType.returnType() != returnType ||
5828 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5829 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5830 }
5831 }
5832 return iterableType; // help the caller a bit
5833 }
5834
5835 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5836 // there should be a better way to uncross my wires
5837 int arity = mh.type().parameterCount();
5838 int[] order = new int[arity];
5839 for (int k = 0; k < arity; k++) order[k] = k;
5840 order[i] = j; order[j] = i;
5841 Class<?>[] types = mh.type().parameterArray();
5842 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5843 MethodType swapType = methodType(mh.type().returnType(), types);
5844 return permuteArguments(mh, swapType, order);
5845 }
5846
5847 /**
5848 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5849 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5850 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5851 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5852 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5853 * {@code try-finally} handle.
5854 * <p>
5855 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5856 * The first is the exception thrown during the
5857 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5858 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5859 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5860 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5861 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5862 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5863 * <p>
5864 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5865 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5866 * two extra leading parameters:<ul>
5867 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5868 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5869 * the result from the execution of the {@code target} handle.
5870 * This parameter is not present if the {@code target} returns {@code void}.
5871 * </ul>
5872 * <p>
5873 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5874 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5875 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5876 * the cleanup.
5877 * <blockquote><pre>{@code
5878 * V target(A..., B...);
5879 * V cleanup(Throwable, V, A...);
5880 * V adapter(A... a, B... b) {
5881 * V result = (zero value for V);
5882 * Throwable throwable = null;
5883 * try {
5884 * result = target(a..., b...);
5885 * } catch (Throwable t) {
5886 * throwable = t;
5887 * throw t;
5888 * } finally {
5889 * result = cleanup(throwable, result, a...);
5890 * }
5891 * return result;
5892 * }
5893 * }</pre></blockquote>
5894 * <p>
5895 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5896 * be modified by execution of the target, and so are passed unchanged
5897 * from the caller to the cleanup, if it is invoked.
5898 * <p>
5899 * The target and cleanup must return the same type, even if the cleanup
5900 * always throws.
5901 * To create such a throwing cleanup, compose the cleanup logic
5902 * with {@link #throwException throwException},
5903 * in order to create a method handle of the correct return type.
5904 * <p>
5905 * Note that {@code tryFinally} never converts exceptions into normal returns.
5906 * In rare cases where exceptions must be converted in that way, first wrap
5907 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
5908 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
5909 * <p>
5910 * It is recommended that the first parameter type of {@code cleanup} be
5911 * declared {@code Throwable} rather than a narrower subtype. This ensures
5912 * {@code cleanup} will always be invoked with whatever exception that
5913 * {@code target} throws. Declaring a narrower type may result in a
5914 * {@code ClassCastException} being thrown by the {@code try-finally}
5915 * handle if the type of the exception thrown by {@code target} is not
5916 * assignable to the first parameter type of {@code cleanup}. Note that
5917 * various exception types of {@code VirtualMachineError},
5918 * {@code LinkageError}, and {@code RuntimeException} can in principle be
5919 * thrown by almost any kind of Java code, and a finally clause that
5920 * catches (say) only {@code IOException} would mask any of the others
5921 * behind a {@code ClassCastException}.
5922 *
5923 * @param target the handle whose execution is to be wrapped in a {@code try} block.
5924 * @param cleanup the handle that is invoked in the finally block.
5925 *
5926 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
5927 * @throws NullPointerException if any argument is null
5928 * @throws IllegalArgumentException if {@code cleanup} does not accept
5929 * the required leading arguments, or if the method handle types do
5930 * not match in their return types and their
5931 * corresponding trailing parameters
5932 *
5933 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
5934 * @since 9
5935 */
5936 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
5937 List<Class<?>> targetParamTypes = target.type().parameterList();
5938 Class<?> rtype = target.type().returnType();
5939
5940 tryFinallyChecks(target, cleanup);
5941
5942 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
5943 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5944 // target parameter list.
5945 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
5946
5947 // Ensure that the intrinsic type checks the instance thrown by the
5948 // target against the first parameter of cleanup
5949 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
5950
5951 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
5952 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
5953 }
5954
5955 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
5956 Class<?> rtype = target.type().returnType();
5957 if (rtype != cleanup.type().returnType()) {
5958 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
5959 }
5960 MethodType cleanupType = cleanup.type();
5961 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
5962 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
5963 }
5964 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
5965 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
5966 }
5967 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5968 // target parameter list.
5969 int cleanupArgIndex = rtype == void.class ? 1 : 2;
5970 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
5971 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5972 cleanup.type(), target.type());
5973 }
5974 }
5975
5976 }
5977