1 /*
2 * Copyright (c) 1997, 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.util;
27
28 /**
29 * This class provides a skeletal implementation of the {@code Collection}
30 * interface, to minimize the effort required to implement this interface. <p>
31 *
32 * To implement an unmodifiable collection, the programmer needs only to
33 * extend this class and provide implementations for the {@code iterator} and
34 * {@code size} methods. (The iterator returned by the {@code iterator}
35 * method must implement {@code hasNext} and {@code next}.)<p>
36 *
37 * To implement a modifiable collection, the programmer must additionally
38 * override this class's {@code add} method (which otherwise throws an
39 * {@code UnsupportedOperationException}), and the iterator returned by the
40 * {@code iterator} method must additionally implement its {@code remove}
41 * method.<p>
42 *
43 * The programmer should generally provide a void (no argument) and
44 * {@code Collection} constructor, as per the recommendation in the
45 * {@code Collection} interface specification.<p>
46 *
47 * The documentation for each non-abstract method in this class describes its
48 * implementation in detail. Each of these methods may be overridden if
49 * the collection being implemented admits a more efficient implementation.<p>
50 *
51 * This class is a member of the
52 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
53 * Java Collections Framework</a>.
54 *
55 * @author Josh Bloch
56 * @author Neal Gafter
57 * @see Collection
58 * @since 1.2
59 */
60
61 public abstract class AbstractCollection<E> implements Collection<E> {
62 /**
63 * Sole constructor. (For invocation by subclass constructors, typically
64 * implicit.)
65 */
66 protected AbstractCollection() {
67 }
68
69 // Query Operations
70
71 /**
72 * Returns an iterator over the elements contained in this collection.
73 *
74 * @return an iterator over the elements contained in this collection
75 */
76 public abstract Iterator<E> iterator();
77
78 public abstract int size();
79
80 /**
81 * {@inheritDoc}
82 *
83 * @implSpec
84 * This implementation returns {@code size() == 0}.
85 */
86 public boolean isEmpty() {
87 return size() == 0;
88 }
89
90 /**
91 * {@inheritDoc}
92 *
93 * @implSpec
94 * This implementation iterates over the elements in the collection,
95 * checking each element in turn for equality with the specified element.
96 *
97 * @throws ClassCastException {@inheritDoc}
98 * @throws NullPointerException {@inheritDoc}
99 */
100 public boolean contains(Object o) {
101 Iterator<E> it = iterator();
102 if (o==null) {
103 while (it.hasNext())
104 if (it.next()==null)
105 return true;
106 } else {
107 while (it.hasNext())
108 if (o.equals(it.next()))
109 return true;
110 }
111 return false;
112 }
113
114 /**
115 * {@inheritDoc}
116 *
117 * @implSpec
118 * This implementation returns an array containing all the elements
119 * returned by this collection's iterator, in the same order, stored in
120 * consecutive elements of the array, starting with index {@code 0}.
121 * The length of the returned array is equal to the number of elements
122 * returned by the iterator, even if the size of this collection changes
123 * during iteration, as might happen if the collection permits
124 * concurrent modification during iteration. The {@code size} method is
125 * called only as an optimization hint; the correct result is returned
126 * even if the iterator returns a different number of elements.
127 *
128 * <p>This method is equivalent to:
129 *
130 * <pre> {@code
131 * List<E> list = new ArrayList<E>(size());
132 * for (E e : this)
133 * list.add(e);
134 * return list.toArray();
135 * }</pre>
136 */
137 public Object[] toArray() {
138 // Estimate size of array; be prepared to see more or fewer elements
139 Object[] r = new Object[size()];
140 Iterator<E> it = iterator();
141 for (int i = 0; i < r.length; i++) {
142 if (! it.hasNext()) // fewer elements than expected
143 return Arrays.copyOf(r, i);
144 r[i] = it.next();
145 }
146 return it.hasNext() ? finishToArray(r, it) : r;
147 }
148
149 /**
150 * {@inheritDoc}
151 *
152 * @implSpec
153 * This implementation returns an array containing all the elements
154 * returned by this collection's iterator in the same order, stored in
155 * consecutive elements of the array, starting with index {@code 0}.
156 * If the number of elements returned by the iterator is too large to
157 * fit into the specified array, then the elements are returned in a
158 * newly allocated array with length equal to the number of elements
159 * returned by the iterator, even if the size of this collection
160 * changes during iteration, as might happen if the collection permits
161 * concurrent modification during iteration. The {@code size} method is
162 * called only as an optimization hint; the correct result is returned
163 * even if the iterator returns a different number of elements.
164 *
165 * <p>This method is equivalent to:
166 *
167 * <pre> {@code
168 * List<E> list = new ArrayList<E>(size());
169 * for (E e : this)
170 * list.add(e);
171 * return list.toArray(a);
172 * }</pre>
173 *
174 * @throws ArrayStoreException {@inheritDoc}
175 * @throws NullPointerException {@inheritDoc}
176 */
177 @SuppressWarnings("unchecked")
178 public <T> T[] toArray(T[] a) {
179 // Estimate size of array; be prepared to see more or fewer elements
180 int size = size();
181 T[] r = a.length >= size ? a :
182 (T[])java.lang.reflect.Array
183 .newInstance(a.getClass().getComponentType(), size);
184 Iterator<E> it = iterator();
185
186 for (int i = 0; i < r.length; i++) {
187 if (! it.hasNext()) { // fewer elements than expected
188 if (a == r) {
189 r[i] = null; // null-terminate
190 } else if (a.length < i) {
191 return Arrays.copyOf(r, i);
192 } else {
193 System.arraycopy(r, 0, a, 0, i);
194 if (a.length > i) {
195 a[i] = null;
196 }
197 }
198 return a;
199 }
200 r[i] = (T)it.next();
201 }
202 // more elements than expected
203 return it.hasNext() ? finishToArray(r, it) : r;
204 }
205
206 /**
207 * The maximum size of array to allocate.
208 * Some VMs reserve some header words in an array.
209 * Attempts to allocate larger arrays may result in
210 * OutOfMemoryError: Requested array size exceeds VM limit
211 */
212 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
213
214 /**
215 * Reallocates the array being used within toArray when the iterator
216 * returned more elements than expected, and finishes filling it from
217 * the iterator.
218 *
219 * @param r the array, replete with previously stored elements
220 * @param it the in-progress iterator over this collection
221 * @return array containing the elements in the given array, plus any
222 * further elements returned by the iterator, trimmed to size
223 */
224 @SuppressWarnings("unchecked")
225 private static <T> T[] finishToArray(T[] r, Iterator<?> it) {
226 int i = r.length;
227 while (it.hasNext()) {
228 int cap = r.length;
229 if (i == cap) {
230 int newCap = cap + (cap >> 1) + 1;
231 // overflow-conscious code
232 if (newCap - MAX_ARRAY_SIZE > 0)
233 newCap = hugeCapacity(cap + 1);
234 r = Arrays.copyOf(r, newCap);
235 }
236 r[i++] = (T)it.next();
237 }
238 // trim if overallocated
239 return (i == r.length) ? r : Arrays.copyOf(r, i);
240 }
241
242 private static int hugeCapacity(int minCapacity) {
243 if (minCapacity < 0) // overflow
244 throw new OutOfMemoryError
245 ("Required array size too large");
246 return (minCapacity > MAX_ARRAY_SIZE) ?
247 Integer.MAX_VALUE :
248 MAX_ARRAY_SIZE;
249 }
250
251 // Modification Operations
252
253 /**
254 * {@inheritDoc}
255 *
256 * @implSpec
257 * This implementation always throws an
258 * {@code UnsupportedOperationException}.
259 *
260 * @throws UnsupportedOperationException {@inheritDoc}
261 * @throws ClassCastException {@inheritDoc}
262 * @throws NullPointerException {@inheritDoc}
263 * @throws IllegalArgumentException {@inheritDoc}
264 * @throws IllegalStateException {@inheritDoc}
265 */
266 public boolean add(E e) {
267 throw new UnsupportedOperationException();
268 }
269
270 /**
271 * {@inheritDoc}
272 *
273 * @implSpec
274 * This implementation iterates over the collection looking for the
275 * specified element. If it finds the element, it removes the element
276 * from the collection using the iterator's remove method.
277 *
278 * <p>Note that this implementation throws an
279 * {@code UnsupportedOperationException} if the iterator returned by this
280 * collection's iterator method does not implement the {@code remove}
281 * method and this collection contains the specified object.
282 *
283 * @throws UnsupportedOperationException {@inheritDoc}
284 * @throws ClassCastException {@inheritDoc}
285 * @throws NullPointerException {@inheritDoc}
286 */
287 public boolean remove(Object o) {
288 Iterator<E> it = iterator();
289 if (o==null) {
290 while (it.hasNext()) {
291 if (it.next()==null) {
292 it.remove();
293 return true;
294 }
295 }
296 } else {
297 while (it.hasNext()) {
298 if (o.equals(it.next())) {
299 it.remove();
300 return true;
301 }
302 }
303 }
304 return false;
305 }
306
307
308 // Bulk Operations
309
310 /**
311 * {@inheritDoc}
312 *
313 * @implSpec
314 * This implementation iterates over the specified collection,
315 * checking each element returned by the iterator in turn to see
316 * if it's contained in this collection. If all elements are so
317 * contained {@code true} is returned, otherwise {@code false}.
318 *
319 * @throws ClassCastException {@inheritDoc}
320 * @throws NullPointerException {@inheritDoc}
321 * @see #contains(Object)
322 */
323 public boolean containsAll(Collection<?> c) {
324 for (Object e : c)
325 if (!contains(e))
326 return false;
327 return true;
328 }
329
330 /**
331 * {@inheritDoc}
332 *
333 * @implSpec
334 * This implementation iterates over the specified collection, and adds
335 * each object returned by the iterator to this collection, in turn.
336 *
337 * <p>Note that this implementation will throw an
338 * {@code UnsupportedOperationException} unless {@code add} is
339 * overridden (assuming the specified collection is non-empty).
340 *
341 * @throws UnsupportedOperationException {@inheritDoc}
342 * @throws ClassCastException {@inheritDoc}
343 * @throws NullPointerException {@inheritDoc}
344 * @throws IllegalArgumentException {@inheritDoc}
345 * @throws IllegalStateException {@inheritDoc}
346 *
347 * @see #add(Object)
348 */
349 public boolean addAll(Collection<? extends E> c) {
350 boolean modified = false;
351 for (E e : c)
352 if (add(e))
353 modified = true;
354 return modified;
355 }
356
357 /**
358 * {@inheritDoc}
359 *
360 * @implSpec
361 * This implementation iterates over this collection, checking each
362 * element returned by the iterator in turn to see if it's contained
363 * in the specified collection. If it's so contained, it's removed from
364 * this collection with the iterator's {@code remove} method.
365 *
366 * <p>Note that this implementation will throw an
367 * {@code UnsupportedOperationException} if the iterator returned by the
368 * {@code iterator} method does not implement the {@code remove} method
369 * and this collection contains one or more elements in common with the
370 * specified collection.
371 *
372 * @throws UnsupportedOperationException {@inheritDoc}
373 * @throws ClassCastException {@inheritDoc}
374 * @throws NullPointerException {@inheritDoc}
375 *
376 * @see #remove(Object)
377 * @see #contains(Object)
378 */
379 public boolean removeAll(Collection<?> c) {
380 Objects.requireNonNull(c);
381 boolean modified = false;
382 Iterator<?> it = iterator();
383 while (it.hasNext()) {
384 if (c.contains(it.next())) {
385 it.remove();
386 modified = true;
387 }
388 }
389 return modified;
390 }
391
392 /**
393 * {@inheritDoc}
394 *
395 * @implSpec
396 * This implementation iterates over this collection, checking each
397 * element returned by the iterator in turn to see if it's contained
398 * in the specified collection. If it's not so contained, it's removed
399 * from this collection with the iterator's {@code remove} method.
400 *
401 * <p>Note that this implementation will throw an
402 * {@code UnsupportedOperationException} if the iterator returned by the
403 * {@code iterator} method does not implement the {@code remove} method
404 * and this collection contains one or more elements not present in the
405 * specified collection.
406 *
407 * @throws UnsupportedOperationException {@inheritDoc}
408 * @throws ClassCastException {@inheritDoc}
409 * @throws NullPointerException {@inheritDoc}
410 *
411 * @see #remove(Object)
412 * @see #contains(Object)
413 */
414 public boolean retainAll(Collection<?> c) {
415 Objects.requireNonNull(c);
416 boolean modified = false;
417 Iterator<E> it = iterator();
418 while (it.hasNext()) {
419 if (!c.contains(it.next())) {
420 it.remove();
421 modified = true;
422 }
423 }
424 return modified;
425 }
426
427 /**
428 * {@inheritDoc}
429 *
430 * @implSpec
431 * This implementation iterates over this collection, removing each
432 * element using the {@code Iterator.remove} operation. Most
433 * implementations will probably choose to override this method for
434 * efficiency.
435 *
436 * <p>Note that this implementation will throw an
437 * {@code UnsupportedOperationException} if the iterator returned by this
438 * collection's {@code iterator} method does not implement the
439 * {@code remove} method and this collection is non-empty.
440 *
441 * @throws UnsupportedOperationException {@inheritDoc}
442 */
443 public void clear() {
444 Iterator<E> it = iterator();
445 while (it.hasNext()) {
446 it.next();
447 it.remove();
448 }
449 }
450
451
452 // String conversion
453
454 /**
455 * Returns a string representation of this collection. The string
456 * representation consists of a list of the collection's elements in the
457 * order they are returned by its iterator, enclosed in square brackets
458 * ({@code "[]"}). Adjacent elements are separated by the characters
459 * {@code ", "} (comma and space). Elements are converted to strings as
460 * by {@link String#valueOf(Object)}.
461 *
462 * @return a string representation of this collection
463 */
464 public String toString() {
465 Iterator<E> it = iterator();
466 if (! it.hasNext())
467 return "[]";
468
469 StringBuilder sb = new StringBuilder();
470 sb.append('[');
471 for (;;) {
472 E e = it.next();
473 sb.append(e == this ? "(this Collection)" : e);
474 if (! it.hasNext())
475 return sb.append(']').toString();
476 sb.append(',').append(' ');
477 }
478 }
479
480 }
481