1 /*
2 * Copyright (c) 2003, 2019, 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 types.
44 *
45 * More information about enums, including descriptions of the
46 * implicitly declared methods synthesized by the compiler, can be
47 * found in section 8.9 of
48 * <cite>The Java™ Language Specification</cite>.
49 *
50 * <p> Note that when using an enumeration type as the type of a set
51 * or as the type of the keys in a map, specialized and efficient
52 * {@linkplain java.util.EnumSet set} and {@linkplain
53 * java.util.EnumMap map} implementations are available.
54 *
55 * @param <E> The enum type subclass
56 * @serial exclude
57 * @author Josh Bloch
58 * @author Neal Gafter
59 * @see Class#getEnumConstants()
60 * @see java.util.EnumSet
61 * @see java.util.EnumMap
62 * @jls 8.9 Enum Types
63 * @jls 8.9.3 Enum Members
64 * @since 1.5
65 */
66 @SuppressWarnings("serial") // No serialVersionUID needed due to
67 // special-casing of enum types.
68 public abstract class Enum<E extends Enum<E>>
69 implements Constable, Comparable<E>, Serializable {
70 /**
71 * The name of this enum constant, as declared in the enum declaration.
72 * Most programmers should use the {@link #toString} method rather than
73 * accessing this field.
74 */
75 private final String name;
76
77 /**
78 * Returns the name of this enum constant, exactly as declared in its
79 * enum declaration.
80 *
81 * <b>Most programmers should use the {@link #toString} method in
82 * preference to this one, as the toString method may return
83 * a more user-friendly name.</b> This method is designed primarily for
84 * use in specialized situations where correctness depends on getting the
85 * exact name, which will not vary from release to release.
86 *
87 * @return the name of this enum constant
88 */
89 public final String name() {
90 return name;
91 }
92
93 /**
94 * The ordinal of this enumeration constant (its position
95 * in the enum declaration, where the initial constant is assigned
96 * an ordinal of zero).
97 *
98 * Most programmers will have no use for this field. It is designed
99 * for use by sophisticated enum-based data structures, such as
100 * {@link java.util.EnumSet} and {@link java.util.EnumMap}.
101 */
102 private final int ordinal;
103
104 /**
105 * Returns the ordinal of this enumeration constant (its position
106 * in its enum declaration, where the initial constant is assigned
107 * an ordinal of zero).
108 *
109 * Most programmers will have no use for this method. It is
110 * designed for use by sophisticated enum-based data structures, such
111 * as {@link java.util.EnumSet} and {@link java.util.EnumMap}.
112 *
113 * @return the ordinal of this enumeration constant
114 */
115 public final int ordinal() {
116 return ordinal;
117 }
118
119 /**
120 * Sole constructor. Programmers cannot invoke this constructor.
121 * It is for use by code emitted by the compiler in response to
122 * enum type declarations.
123 *
124 * @param name - The name of this enum constant, which is the identifier
125 * used to declare it.
126 * @param ordinal - The ordinal of this enumeration constant (its position
127 * in the enum declaration, where the initial constant is assigned
128 * an ordinal of zero).
129 */
130 protected Enum(String name, int ordinal) {
131 this.name = name;
132 this.ordinal = ordinal;
133 }
134
135 /**
136 * Returns the name of this enum constant, as contained in the
137 * declaration. This method may be overridden, though it typically
138 * isn't necessary or desirable. An enum type should override this
139 * method when a more "programmer-friendly" string form exists.
140 *
141 * @return the name of this enum constant
142 */
143 public String toString() {
144 return name;
145 }
146
147 /**
148 * Returns true if the specified object is equal to this
149 * enum constant.
150 *
151 * @param other the object to be compared for equality with this object.
152 * @return true if the specified object is equal to this
153 * enum constant.
154 */
155 public final boolean equals(Object other) {
156 return this==other;
157 }
158
159 /**
160 * Returns a hash code for this enum constant.
161 *
162 * @return a hash code for this enum constant.
163 */
164 public final int hashCode() {
165 return super.hashCode();
166 }
167
168 /**
169 * Throws CloneNotSupportedException. This guarantees that enums
170 * are never cloned, which is necessary to preserve their "singleton"
171 * status.
172 *
173 * @return (never returns)
174 */
175 protected final Object clone() throws CloneNotSupportedException {
176 throw new CloneNotSupportedException();
177 }
178
179 /**
180 * Compares this enum with the specified object for order. Returns a
181 * negative integer, zero, or a positive integer as this object is less
182 * than, equal to, or greater than the specified object.
183 *
184 * Enum constants are only comparable to other enum constants of the
185 * same enum type. The natural order implemented by this
186 * method is the order in which the constants are declared.
187 */
188 public final int compareTo(E o) {
189 Enum<?> other = (Enum<?>)o;
190 Enum<E> self = this;
191 if (self.getClass() != other.getClass() && // optimization
192 self.getDeclaringClass() != other.getDeclaringClass())
193 throw new ClassCastException();
194 return self.ordinal - other.ordinal;
195 }
196
197 /**
198 * Returns the Class object corresponding to this enum constant's
199 * enum type. Two enum constants e1 and e2 are of the
200 * same enum type if and only if
201 * e1.getDeclaringClass() == e2.getDeclaringClass().
202 * (The value returned by this method may differ from the one returned
203 * by the {@link Object#getClass} method for enum constants with
204 * constant-specific class bodies.)
205 *
206 * @return the Class object corresponding to this enum constant's
207 * enum type
208 */
209 @SuppressWarnings("unchecked")
210 public final Class<E> getDeclaringClass() {
211 Class<?> clazz = getClass();
212 Class<?> zuper = clazz.getSuperclass();
213 return (zuper == Enum.class) ? (Class<E>)clazz : (Class<E>)zuper;
214 }
215
216 /**
217 * Returns an enum descriptor {@code EnumDesc} for this instance, if one can be
218 * constructed, or an empty {@link Optional} if one cannot be.
219 *
220 * @return An {@link Optional} containing the resulting nominal descriptor,
221 * or an empty {@link Optional} if one cannot be constructed.
222 * @since 12
223 */
224 @Override
225 public final Optional<EnumDesc<E>> describeConstable() {
226 return getDeclaringClass()
227 .describeConstable()
228 .map(c -> EnumDesc.of(c, name));
229 }
230
231 /**
232 * Returns the enum constant of the specified enum type with the
233 * specified name. The name must match exactly an identifier used
234 * to declare an enum constant in this type. (Extraneous whitespace
235 * characters are not permitted.)
236 *
237 * <p>Note that for a particular enum type {@code T}, the
238 * implicitly declared {@code public static T valueOf(String)}
239 * method on that enum may be used instead of this method to map
240 * from a name to the corresponding enum constant. All the
241 * constants of an enum type can be obtained by calling the
242 * implicit {@code public static T[] values()} method of that
243 * type.
244 *
245 * @param <T> The enum type whose constant is to be returned
246 * @param enumType the {@code Class} object of the enum type from which
247 * to return a constant
248 * @param name the name of the constant to return
249 * @return the enum constant of the specified enum type with the
250 * specified name
251 * @throws IllegalArgumentException if the specified enum type has
252 * no constant with the specified name, or the specified
253 * class object does not represent an enum type
254 * @throws NullPointerException if {@code enumType} or {@code name}
255 * is null
256 * @since 1.5
257 */
258 public static <T extends Enum<T>> T valueOf(Class<T> enumType,
259 String name) {
260 T result = enumType.enumConstantDirectory().get(name);
261 if (result != null)
262 return result;
263 if (name == null)
264 throw new NullPointerException("Name is null");
265 throw new IllegalArgumentException(
266 "No enum constant " + enumType.getCanonicalName() + "." + name);
267 }
268
269 /**
270 * enum classes cannot have finalize methods.
271 */
272 @SuppressWarnings("deprecation")
273 protected final void finalize() { }
274
275 /**
276 * prevent default deserialization
277 */
278 private void readObject(ObjectInputStream in) throws IOException,
279 ClassNotFoundException {
280 throw new InvalidObjectException("can't deserialize enum");
281 }
282
283 private void readObjectNoData() throws ObjectStreamException {
284 throw new InvalidObjectException("can't deserialize enum");
285 }
286
287 /**
288 * A <a href="{@docRoot}/java.base/java/lang/constant/package-summary.html#nominal">nominal descriptor</a> for an
289 * {@code enum} constant.
290 *
291 * @param <E> the type of the enum constant
292 *
293 * @since 12
294 */
295 public static final class EnumDesc<E extends Enum<E>>
296 extends DynamicConstantDesc<E> {
297
298 /**
299 * Constructs a nominal descriptor for the specified {@code enum} class and name.
300 *
301 * @param constantType a {@link ClassDesc} describing the {@code enum} class
302 * @param constantName the unqualified name of the enum constant
303 * @throws NullPointerException if any argument is null
304 * @jvms 4.2.2 Unqualified Names
305 */
306 private EnumDesc(ClassDesc constantType, String constantName) {
307 super(ConstantDescs.BSM_ENUM_CONSTANT, requireNonNull(constantName), requireNonNull(constantType));
308 }
309
310 /**
311 * Returns a nominal descriptor for the specified {@code enum} class and name
312 *
313 * @param <E> the type of the enum constant
314 * @param enumClass a {@link ClassDesc} describing the {@code enum} class
315 * @param constantName the unqualified name of the enum constant
316 * @return the nominal descriptor
317 * @throws NullPointerException if any argument is null
318 * @jvms 4.2.2 Unqualified Names
319 * @since 12
320 */
321 public static<E extends Enum<E>> EnumDesc<E> of(ClassDesc enumClass,
322 String constantName) {
323 return new EnumDesc<>(enumClass, constantName);
324 }
325
326 @Override
327 @SuppressWarnings("unchecked")
328 public E resolveConstantDesc(MethodHandles.Lookup lookup)
329 throws ReflectiveOperationException {
330 return Enum.valueOf((Class<E>) constantType().resolveConstantDesc(lookup), constantName());
331 }
332
333 @Override
334 public String toString() {
335 return String.format("EnumDesc[%s.%s]", constantType().displayName(), constantName());
336 }
337 }
338 }