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