1 /*
2 * Copyright (c) 2003, 2009, 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 public abstract class Enum<E extends Enum<E>>
56 implements Comparable<E>, Serializable {
57 /**
58 * The name of this enum constant, as declared in the enum declaration.
59 * Most programmers should use the {@link #toString} method rather than
60 * accessing this field.
61 */
62 private final String name;
63
64 /**
65 * Returns the name of this enum constant, exactly as declared in its
66 * enum declaration.
67 *
68 * <b>Most programmers should use the {@link #toString} method in
69 * preference to this one, as the toString method may return
70 * a more user-friendly name.</b> This method is designed primarily for
71 * use in specialized situations where correctness depends on getting the
72 * exact name, which will not vary from release to release.
73 *
74 * @return the name of this enum constant
75 */
76 public final String name() {
77 return name;
78 }
79
80 /**
81 * The ordinal of this enumeration constant (its position
82 * in the enum declaration, where the initial constant is assigned
83 * an ordinal of zero).
84 *
85 * Most programmers will have no use for this field. It is designed
86 * for use by sophisticated enum-based data structures, such as
87 * {@link java.util.EnumSet} and {@link java.util.EnumMap}.
88 */
89 private final int ordinal;
90
91 /**
92 * Returns the ordinal of this enumeration constant (its position
93 * in its enum declaration, where the initial constant is assigned
94 * an ordinal of zero).
95 *
96 * Most programmers will have no use for this method. It is
97 * designed for use by sophisticated enum-based data structures, such
98 * as {@link java.util.EnumSet} and {@link java.util.EnumMap}.
99 *
100 * @return the ordinal of this enumeration constant
101 */
102 public final int ordinal() {
103 return ordinal;
104 }
105
106 /**
107 * Sole constructor. Programmers cannot invoke this constructor.
108 * It is for use by code emitted by the compiler in response to
109 * enum type declarations.
110 *
111 * @param name - The name of this enum constant, which is the identifier
112 * used to declare it.
113 * @param ordinal - The ordinal of this enumeration constant (its position
114 * in the enum declaration, where the initial constant is assigned
115 * an ordinal of zero).
116 */
117 protected Enum(String name, int ordinal) {
118 this.name = name;
119 this.ordinal = ordinal;
120 }
121
122 /**
123 * Returns the name of this enum constant, as contained in the
124 * declaration. This method may be overridden, though it typically
125 * isn't necessary or desirable. An enum type should override this
126 * method when a more "programmer-friendly" string form exists.
127 *
128 * @return the name of this enum constant
129 */
130 public String toString() {
131 return name;
132 }
133
134 /**
135 * Returns true if the specified object is equal to this
136 * enum constant.
137 *
138 * @param other the object to be compared for equality with this object.
139 * @return true if the specified object is equal to this
140 * enum constant.
141 */
142 public final boolean equals(Object other) {
143 return this==other;
144 }
145
146 /**
147 * Returns a hash code for this enum constant.
148 *
149 * @return a hash code for this enum constant.
150 */
151 public final int hashCode() {
152 return super.hashCode();
153 }
154
155 /**
156 * Throws CloneNotSupportedException. This guarantees that enums
157 * are never cloned, which is necessary to preserve their "singleton"
158 * status.
159 *
160 * @return (never returns)
161 */
162 protected final Object clone() throws CloneNotSupportedException {
163 throw new CloneNotSupportedException();
164 }
165
166 /**
167 * Compares this enum with the specified object for order. Returns a
168 * negative integer, zero, or a positive integer as this object is less
169 * than, equal to, or greater than the specified object.
170 *
171 * Enum constants are only comparable to other enum constants of the
172 * same enum type. The natural order implemented by this
173 * method is the order in which the constants are declared.
174 */
175 public final int compareTo(E o) {
176 Enum other = (Enum)o;
177 Enum self = this;
178 if (self.getClass() != other.getClass() && // optimization
179 self.getDeclaringClass() != other.getDeclaringClass())
180 throw new ClassCastException();
181 return self.ordinal - other.ordinal;
182 }
183
184 /**
185 * Returns the Class object corresponding to this enum constant's
186 * enum type. Two enum constants e1 and e2 are of the
187 * same enum type if and only if
188 * e1.getDeclaringClass() == e2.getDeclaringClass().
189 * (The value returned by this method may differ from the one returned
190 * by the {@link Object#getClass} method for enum constants with
191 * constant-specific class bodies.)
192 *
193 * @return the Class object corresponding to this enum constant's
194 * enum type
195 */
196 public final Class<E> getDeclaringClass() {
197 Class clazz = getClass();
198 Class zuper = clazz.getSuperclass();
199 return (zuper == Enum.class) ? clazz : zuper;
200 }
201
202 /**
203 * Returns the enum constant of the specified enum type with the
204 * specified name. The name must match exactly an identifier used
205 * to declare an enum constant in this type. (Extraneous whitespace
206 * characters are not permitted.)
207 *
208 * <p>Note that for a particular enum type {@code T}, the
209 * implicitly declared {@code public static T valueOf(String)}
210 * method on that enum may be used instead of this method to map
211 * from a name to the corresponding enum constant. All the
212 * constants of an enum type can be obtained by calling the
213 * implicit {@code public static T[] values()} method of that
214 * type.
215 *
216 * @param <T> The enum type whose constant is to be returned
217 * @param enumType the {@code Class} object of the enum type from which
218 * to return a constant
219 * @param name the name of the constant to return
220 * @return the enum constant of the specified enum type with the
221 * specified name
222 * @throws IllegalArgumentException if the specified enum type has
223 * no constant with the specified name, or the specified
224 * class object does not represent an enum type
225 * @throws NullPointerException if {@code enumType} or {@code name}
226 * is null
227 * @since 1.5
228 */
229 public static <T extends Enum<T>> T valueOf(Class<T> enumType,
230 String name) {
231 T result = enumType.enumConstantDirectory().get(name);
232 if (result != null)
233 return result;
234 if (name == null)
235 throw new NullPointerException("Name is null");
236 throw new IllegalArgumentException(
237 "No enum constant " + enumType.getCanonicalName() + "." + name);
238 }
239
240 /**
241 * enum classes cannot have finalize methods.
242 */
243 protected final void finalize() { }
244
245 /**
246 * prevent default deserialization
247 */
248 private void readObject(ObjectInputStream in) throws IOException,
249 ClassNotFoundException {
250 throw new InvalidObjectException("can't deserialize enum");
251 }
252
253 private void readObjectNoData() throws ObjectStreamException {
254 throw new InvalidObjectException("can't deserialize enum");
255 }
256 }