1 /*
2 * Copyright (c) 2003, 2020, 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.IOException;
29 import java.io.InvalidObjectException;
30 import java.io.ObjectInputStream;
31 import java.io.ObjectStreamException;
32 import java.io.Serializable;
33 import java.lang.constant.ClassDesc;
34 import java.lang.constant.Constable;
35 import java.lang.constant.ConstantDescs;
36 import java.lang.constant.DynamicConstantDesc;
37 import java.lang.invoke.MethodHandles;
38 import java.util.Optional;
39
40 import static java.util.Objects.requireNonNull;
41
42 /**
43 * This is the common base class of all Java language enumeration classes.
44 *
45 * More information about enums, including descriptions of the
46 * implicitly declared methods synthesized by the compiler, can be
47 * found in section {@jls 8.9} of <cite>The Java Language
48 * Specification</cite>.
49 *
50 * Enumeration classes are all serializable and receive special handling
51 * by the serialization mechanism. The serialized representation used
52 * for enum constants cannot be customized. Declarations of methods
53 * and fields that would otherwise interact with serialization are
54 * ignored, including {@code serialVersionUID}; see the <cite>Java
55 * Object Serialization Specification</cite> for details.
56 *
57 * <p> Note that when using an enumeration type as the type of a set
58 * or as the type of the keys in a map, specialized and efficient
59 * {@linkplain java.util.EnumSet set} and {@linkplain
60 * java.util.EnumMap map} implementations are available.
61 *
62 * @param <E> The type of the enum subclass
63 * @serial exclude
64 * @author Josh Bloch
65 * @author Neal Gafter
66 * @see Class#getEnumConstants()
67 * @see java.util.EnumSet
68 * @see java.util.EnumMap
69 * @jls 8.9 Enum Classes
70 * @jls 8.9.3 Enum Members
71 * @since 1.5
72 */
73 @SuppressWarnings("serial") // No serialVersionUID needed due to
74 // special-casing of enum classes.
75 public abstract class Enum<E extends Enum<E>>
76 implements Constable, Comparable<E>, Serializable {
77 /**
78 * The name of this enum constant, as declared in the enum declaration.
79 * Most programmers should use the {@link #toString} method rather than
80 * accessing this field.
81 */
82 private final String name;
83
84 /**
85 * Returns the name of this enum constant, exactly as declared in its
86 * enum declaration.
87 *
88 * <b>Most programmers should use the {@link #toString} method in
89 * preference to this one, as the toString method may return
90 * a more user-friendly name.</b> This method is designed primarily for
91 * use in specialized situations where correctness depends on getting the
92 * exact name, which will not vary from release to release.
93 *
94 * @return the name of this enum constant
95 */
96 public final String name() {
97 return name;
98 }
99
100 /**
101 * The ordinal of this enumeration constant (its position
102 * in the enum declaration, where the initial constant is assigned
103 * an ordinal of zero).
104 *
105 * Most programmers will have no use for this field. It is designed
106 * for use by sophisticated enum-based data structures, such as
107 * {@link java.util.EnumSet} and {@link java.util.EnumMap}.
108 */
109 private final int ordinal;
110
111 /**
112 * Returns the ordinal of this enumeration constant (its position
113 * in its enum declaration, where the initial constant is assigned
114 * an ordinal of zero).
115 *
116 * Most programmers will have no use for this method. It is
117 * designed for use by sophisticated enum-based data structures, such
118 * as {@link java.util.EnumSet} and {@link java.util.EnumMap}.
119 *
120 * @return the ordinal of this enumeration constant
121 */
122 public final int ordinal() {
123 return ordinal;
124 }
125
126 /**
127 * Sole constructor. Programmers cannot invoke this constructor.
128 * It is for use by code emitted by the compiler in response to
129 * enum class declarations.
130 *
131 * @param name - The name of this enum constant, which is the identifier
132 * used to declare it.
133 * @param ordinal - The ordinal of this enumeration constant (its position
134 * in the enum declaration, where the initial constant is assigned
135 * an ordinal of zero).
136 */
137 protected Enum(String name, int ordinal) {
138 this.name = name;
139 this.ordinal = ordinal;
140 }
141
142 /**
143 * Returns the name of this enum constant, as contained in the
144 * declaration. This method may be overridden, though it typically
145 * isn't necessary or desirable. An enum class should override this
146 * method when a more "programmer-friendly" string form exists.
147 *
148 * @return the name of this enum constant
149 */
150 public String toString() {
151 return name;
152 }
153
154 /**
155 * Returns true if the specified object is equal to this
156 * enum constant.
157 *
158 * @param other the object to be compared for equality with this object.
159 * @return true if the specified object is equal to this
160 * enum constant.
161 */
162 public final boolean equals(Object other) {
163 return this==other;
164 }
165
166 /**
167 * Returns a hash code for this enum constant.
168 *
169 * @return a hash code for this enum constant.
170 */
171 public final int hashCode() {
172 return super.hashCode();
173 }
174
175 /**
176 * Throws CloneNotSupportedException. This guarantees that enums
177 * are never cloned, which is necessary to preserve their "singleton"
178 * status.
179 *
180 * @return (never returns)
181 */
182 protected final Object clone() throws CloneNotSupportedException {
183 throw new CloneNotSupportedException();
184 }
185
186 /**
187 * Compares this enum with the specified object for order. Returns a
188 * negative integer, zero, or a positive integer as this object is less
189 * than, equal to, or greater than the specified object.
190 *
191 * Enum constants are only comparable to other enum constants of the
192 * same enum type. The natural order implemented by this
193 * method is the order in which the constants are declared.
194 */
195 public final int compareTo(E o) {
196 Enum<?> other = (Enum<?>)o;
197 Enum<E> self = this;
198 if (self.getClass() != other.getClass() && // optimization
199 self.getDeclaringClass() != other.getDeclaringClass())
200 throw new ClassCastException();
201 return self.ordinal - other.ordinal;
202 }
203
204 /**
205 * Returns the Class object corresponding to this enum constant's
206 * enum type. Two enum constants e1 and e2 are of the
207 * same enum type if and only if
208 * e1.getDeclaringClass() == e2.getDeclaringClass().
209 * (The value returned by this method may differ from the one returned
210 * by the {@link Object#getClass} method for enum constants with
211 * constant-specific class bodies.)
212 *
213 * @return the Class object corresponding to this enum constant's
214 * enum type
215 */
216 @SuppressWarnings("unchecked")
217 public final Class<E> getDeclaringClass() {
218 Class<?> clazz = getClass();
219 Class<?> zuper = clazz.getSuperclass();
220 return (zuper == Enum.class) ? (Class<E>)clazz : (Class<E>)zuper;
221 }
222
223 /**
224 * Returns an enum descriptor {@code EnumDesc} for this instance, if one can be
225 * constructed, or an empty {@link Optional} if one cannot be.
226 *
227 * @return An {@link Optional} containing the resulting nominal descriptor,
228 * or an empty {@link Optional} if one cannot be constructed.
229 * @since 12
230 */
231 @Override
232 public final Optional<EnumDesc<E>> describeConstable() {
233 return getDeclaringClass()
234 .describeConstable()
235 .map(c -> EnumDesc.of(c, name));
236 }
237
238 /**
239 * Returns the enum constant of the specified enum class with the
240 * specified name. The name must match exactly an identifier used
241 * to declare an enum constant in this class. (Extraneous whitespace
242 * characters are not permitted.)
243 *
244 * <p>Note that for a particular enum class {@code T}, the
245 * implicitly declared {@code public static T valueOf(String)}
246 * method on that enum may be used instead of this method to map
247 * from a name to the corresponding enum constant. All the
248 * constants of an enum class can be obtained by calling the
249 * implicit {@code public static T[] values()} method of that
250 * class.
251 *
252 * @param <T> The enum class whose constant is to be returned
253 * @param enumClass the {@code Class} object of the enum class from which
254 * to return a constant
255 * @param name the name of the constant to return
256 * @return the enum constant of the specified enum class with the
257 * specified name
258 * @throws IllegalArgumentException if the specified enum class has
259 * no constant with the specified name, or the specified
260 * class object does not represent an enum class
261 * @throws NullPointerException if {@code enumClass} or {@code name}
262 * is null
263 * @since 1.5
264 */
265 public static <T extends Enum<T>> T valueOf(Class<T> enumClass,
266 String name) {
267 T result = enumClass.enumConstantDirectory().get(name);
268 if (result != null)
269 return result;
270 if (name == null)
271 throw new NullPointerException("Name is null");
272 throw new IllegalArgumentException(
273 "No enum constant " + enumClass.getCanonicalName() + "." + name);
274 }
275
276 /**
277 * enum classes cannot have finalize methods.
278 */
279 @SuppressWarnings("deprecation")
280 protected final void finalize() { }
281
282 /**
283 * prevent default deserialization
284 */
285 @java.io.Serial
286 private void readObject(ObjectInputStream in) throws IOException,
287 ClassNotFoundException {
288 throw new InvalidObjectException("can't deserialize enum");
289 }
290
291 @java.io.Serial
292 private void readObjectNoData() throws ObjectStreamException {
293 throw new InvalidObjectException("can't deserialize enum");
294 }
295
296 /**
297 * A <a href="{@docRoot}/java.base/java/lang/constant/package-summary.html#nominal">nominal descriptor</a> for an
298 * {@code enum} constant.
299 *
300 * @param <E> the type of the enum constant
301 *
302 * @since 12
303 */
304 public static final class EnumDesc<E extends Enum<E>>
305 extends DynamicConstantDesc<E> {
306
307 /**
308 * Constructs a nominal descriptor for the specified {@code enum} class and name.
309 *
310 * @param constantClass a {@link ClassDesc} describing the {@code enum} class
311 * @param constantName the unqualified name of the enum constant
312 * @throws NullPointerException if any argument is null
313 * @jvms 4.2.2 Unqualified Names
314 */
315 private EnumDesc(ClassDesc constantClass, String constantName) {
316 super(ConstantDescs.BSM_ENUM_CONSTANT, requireNonNull(constantName), requireNonNull(constantClass));
317 }
318
319 /**
320 * Returns a nominal descriptor for the specified {@code enum} class and name
321 *
322 * @param <E> the type of the enum constant
323 * @param enumClass a {@link ClassDesc} describing the {@code enum} class
324 * @param constantName the unqualified name of the enum constant
325 * @return the nominal descriptor
326 * @throws NullPointerException if any argument is null
327 * @jvms 4.2.2 Unqualified Names
328 * @since 12
329 */
330 public static<E extends Enum<E>> EnumDesc<E> of(ClassDesc enumClass,
331 String constantName) {
332 return new EnumDesc<>(enumClass, constantName);
333 }
334
335 @Override
336 @SuppressWarnings("unchecked")
337 public E resolveConstantDesc(MethodHandles.Lookup lookup)
338 throws ReflectiveOperationException {
339 return Enum.valueOf((Class<E>) constantType().resolveConstantDesc(lookup), constantName());
340 }
341
342 @Override
343 public String toString() {
344 return String.format("EnumDesc[%s.%s]", constantType().displayName(), constantName());
345 }
346 }
347 }