1 /*
2 * Copyright (c) 2003, 2017, 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;
27
28 import java.io.Serializable;
29 import java.io.IOException;
30 import java.io.InvalidObjectException;
31 import java.io.ObjectInputStream;
32 import java.io.ObjectStreamException;
33
34 /**
35 * This is the common base class of all Java language enumeration types.
36 *
37 * More information about enums, including descriptions of the
38 * implicitly declared methods synthesized by the compiler, can be
39 * found in section 8.9 of
40 * <cite>The Java™ Language Specification</cite>.
41 *
42 * <p> Note that when using an enumeration type as the type of a set
43 * or as the type of the keys in a map, specialized and efficient
44 * {@linkplain java.util.EnumSet set} and {@linkplain
45 * java.util.EnumMap map} implementations are available.
46 *
47 * @param <E> The enum type subclass
48 * @author Josh Bloch
49 * @author Neal Gafter
50 * @see Class#getEnumConstants()
51 * @see java.util.EnumSet
52 * @see java.util.EnumMap
53 * @since 1.5
54 */
55 @SuppressWarnings("serial") // No serialVersionUID needed due to
56 // special-casing of enum types.
57 public abstract class Enum<E extends Enum<E>>
58 implements Comparable<E>, Serializable {
59 /**
60 * The name of this enum constant, as declared in the enum declaration.
61 * Most programmers should use the {@link #toString} method rather than
62 * accessing this field.
63 */
64 private final String name;
65
66 /**
67 * Returns the name of this enum constant, exactly as declared in its
68 * enum declaration.
69 *
70 * <b>Most programmers should use the {@link #toString} method in
71 * preference to this one, as the toString method may return
72 * a more user-friendly name.</b> This method is designed primarily for
73 * use in specialized situations where correctness depends on getting the
74 * exact name, which will not vary from release to release.
75 *
76 * @return the name of this enum constant
77 */
78 public final String name() {
79 return name;
80 }
81
82 /**
83 * The ordinal of this enumeration constant (its position
84 * in the enum declaration, where the initial constant is assigned
85 * an ordinal of zero).
86 *
87 * Most programmers will have no use for this field. It is designed
88 * for use by sophisticated enum-based data structures, such as
89 * {@link java.util.EnumSet} and {@link java.util.EnumMap}.
90 */
91 private final int ordinal;
92
93 /**
94 * Returns the ordinal of this enumeration constant (its position
95 * in its enum declaration, where the initial constant is assigned
96 * an ordinal of zero).
97 *
98 * Most programmers will have no use for this method. It is
99 * designed for use by sophisticated enum-based data structures, such
100 * as {@link java.util.EnumSet} and {@link java.util.EnumMap}.
101 *
102 * @return the ordinal of this enumeration constant
103 */
104 public final int ordinal() {
105 return ordinal;
106 }
107
108 /**
109 * Sole constructor. Programmers cannot invoke this constructor.
110 * It is for use by code emitted by the compiler in response to
111 * enum type declarations.
112 *
113 * @param name - The name of this enum constant, which is the identifier
114 * used to declare it.
115 * @param ordinal - The ordinal of this enumeration constant (its position
116 * in the enum declaration, where the initial constant is assigned
117 * an ordinal of zero).
118 */
119 protected Enum(String name, int ordinal) {
120 this.name = name;
121 this.ordinal = ordinal;
122 }
123
124 /**
125 * Returns the name of this enum constant, as contained in the
126 * declaration. This method may be overridden, though it typically
127 * isn't necessary or desirable. An enum type should override this
128 * method when a more "programmer-friendly" string form exists.
129 *
130 * @return the name of this enum constant
131 */
132 public String toString() {
133 return name;
134 }
135
136 /**
137 * Returns true if the specified object is equal to this
138 * enum constant.
139 *
140 * @param other the object to be compared for equality with this object.
141 * @return true if the specified object is equal to this
142 * enum constant.
143 */
144 public final boolean equals(Object other) {
145 return this==other;
146 }
147
148 /**
149 * Returns a hash code for this enum constant.
150 *
151 * @return a hash code for this enum constant.
152 */
153 public final int hashCode() {
154 return super.hashCode();
155 }
156
157 /**
158 * Throws CloneNotSupportedException. This guarantees that enums
159 * are never cloned, which is necessary to preserve their "singleton"
160 * status.
161 *
162 * @return (never returns)
163 */
164 protected final Object clone() throws CloneNotSupportedException {
165 throw new CloneNotSupportedException();
166 }
167
168 /**
169 * Compares this enum with the specified object for order. Returns a
170 * negative integer, zero, or a positive integer as this object is less
171 * than, equal to, or greater than the specified object.
172 *
173 * Enum constants are only comparable to other enum constants of the
174 * same enum type. The natural order implemented by this
175 * method is the order in which the constants are declared.
176 */
177 public final int compareTo(E o) {
178 Enum<?> other = (Enum<?>)o;
179 Enum<E> self = this;
180 if (self.getClass() != other.getClass() && // optimization
181 self.getDeclaringClass() != other.getDeclaringClass())
182 throw new ClassCastException();
183 return self.ordinal - other.ordinal;
184 }
185
186 /**
187 * Returns the Class object corresponding to this enum constant's
188 * enum type. Two enum constants e1 and e2 are of the
189 * same enum type if and only if
190 * e1.getDeclaringClass() == e2.getDeclaringClass().
191 * (The value returned by this method may differ from the one returned
192 * by the {@link Object#getClass} method for enum constants with
193 * constant-specific class bodies.)
194 *
195 * @return the Class object corresponding to this enum constant's
196 * enum type
197 */
198 @SuppressWarnings("unchecked")
199 public final Class<E> getDeclaringClass() {
200 Class<?> clazz = getClass();
201 Class<?> zuper = clazz.getSuperclass();
202 return (zuper == Enum.class) ? (Class<E>)clazz : (Class<E>)zuper;
203 }
204
205 /**
206 * Returns the enum constant of the specified enum type with the
207 * specified name. The name must match exactly an identifier used
208 * to declare an enum constant in this type. (Extraneous whitespace
209 * characters are not permitted.)
210 *
211 * <p>Note that for a particular enum type {@code T}, the
212 * implicitly declared {@code public static T valueOf(String)}
213 * method on that enum may be used instead of this method to map
214 * from a name to the corresponding enum constant. All the
215 * constants of an enum type can be obtained by calling the
216 * implicit {@code public static T[] values()} method of that
217 * type.
218 *
219 * @param <T> The enum type whose constant is to be returned
220 * @param enumType the {@code Class} object of the enum type from which
221 * to return a constant
222 * @param name the name of the constant to return
223 * @return the enum constant of the specified enum type with the
224 * specified name
225 * @throws IllegalArgumentException if the specified enum type has
226 * no constant with the specified name, or the specified
227 * class object does not represent an enum type
228 * @throws NullPointerException if {@code enumType} or {@code name}
229 * is null
230 * @since 1.5
231 */
232 public static <T extends Enum<T>> T valueOf(Class<T> enumType,
233 String name) {
234 T result = enumType.enumConstantDirectory().get(name);
235 if (result != null)
236 return result;
237 if (name == null)
238 throw new NullPointerException("Name is null");
239 throw new IllegalArgumentException(
240 "No enum constant " + enumType.getCanonicalName() + "." + name);
241 }
242
243 /**
244 * enum classes cannot have finalize methods.
245 */
246 @SuppressWarnings("deprecation")
247 protected final void finalize() { }
248
249 /**
250 * prevent default deserialization
251 */
252 private void readObject(ObjectInputStream in) throws IOException,
253 ClassNotFoundException {
254 throw new InvalidObjectException("can't deserialize enum");
255 }
256
257 private void readObjectNoData() throws ObjectStreamException {
258 throw new InvalidObjectException("can't deserialize enum");
259 }
260 }
261