1 /*
2 * Copyright 2003-2009 Sun Microsystems, Inc. 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. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any 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 implicit methods synthesised
38 * by the compiler, can be found in <i>The Java™ Language
39 * Specification, Third Edition</i>, <a
40 * href="http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.9">§8.9</a>.
41 *
42 * @author Josh Bloch
43 * @author Neal Gafter
44 * @see Class#getEnumConstants()
45 * @since 1.5
46 */
47 public abstract class Enum<E extends Enum<E>>
48 implements Comparable<E>, Serializable {
49 /**
50 * The name of this enum constant, as declared in the enum declaration.
51 * Most programmers should use the {@link #toString} method rather than
52 * accessing this field.
53 */
54 private final String name;
55
56 /**
57 * Returns the name of this enum constant, exactly as declared in its
58 * enum declaration.
59 *
60 * <b>Most programmers should use the {@link #toString} method in
61 * preference to this one, as the toString method may return
62 * a more user-friendly name.</b> This method is designed primarily for
63 * use in specialized situations where correctness depends on getting the
64 * exact name, which will not vary from release to release.
65 *
66 * @return the name of this enum constant
67 */
68 public final String name() {
69 return name;
70 }
71
72 /**
73 * The ordinal of this enumeration constant (its position
74 * in the enum declaration, where the initial constant is assigned
75 * an ordinal of zero).
76 *
77 * Most programmers will have no use for this field. It is designed
78 * for use by sophisticated enum-based data structures, such as
79 * {@link java.util.EnumSet} and {@link java.util.EnumMap}.
80 */
81 private final int ordinal;
82
83 /**
84 * Returns the ordinal of this enumeration constant (its position
85 * in its enum declaration, where the initial constant is assigned
86 * an ordinal of zero).
87 *
88 * Most programmers will have no use for this method. It is
89 * designed for use by sophisticated enum-based data structures, such
90 * as {@link java.util.EnumSet} and {@link java.util.EnumMap}.
91 *
92 * @return the ordinal of this enumeration constant
93 */
94 public final int ordinal() {
95 return ordinal;
96 }
97
98 /**
99 * Sole constructor. Programmers cannot invoke this constructor.
100 * It is for use by code emitted by the compiler in response to
101 * enum type declarations.
102 *
103 * @param name - The name of this enum constant, which is the identifier
104 * used to declare it.
105 * @param ordinal - The ordinal of this enumeration constant (its position
106 * in the enum declaration, where the initial constant is assigned
107 * an ordinal of zero).
108 */
109 protected Enum(String name, int ordinal) {
110 this.name = name;
111 this.ordinal = ordinal;
112 }
113
114 /**
115 * Returns the name of this enum constant, as contained in the
116 * declaration. This method may be overridden, though it typically
117 * isn't necessary or desirable. An enum type should override this
118 * method when a more "programmer-friendly" string form exists.
119 *
120 * @return the name of this enum constant
121 */
122 public String toString() {
123 return name;
124 }
125
126 /**
127 * Returns true if the specified object is equal to this
128 * enum constant.
129 *
130 * @param other the object to be compared for equality with this object.
131 * @return true if the specified object is equal to this
132 * enum constant.
133 */
134 public final boolean equals(Object other) {
135 return this==other;
136 }
137
138 /**
139 * Returns a hash code for this enum constant.
140 *
141 * @return a hash code for this enum constant.
142 */
143 public final int hashCode() {
144 return super.hashCode();
145 }
146
147 /**
148 * Throws CloneNotSupportedException. This guarantees that enums
149 * are never cloned, which is necessary to preserve their "singleton"
150 * status.
151 *
152 * @return (never returns)
153 */
154 protected final Object clone() throws CloneNotSupportedException {
155 throw new CloneNotSupportedException();
156 }
157
158 /**
159 * Compares this enum with the specified object for order. Returns a
160 * negative integer, zero, or a positive integer as this object is less
161 * than, equal to, or greater than the specified object.
162 *
163 * Enum constants are only comparable to other enum constants of the
164 * same enum type. The natural order implemented by this
165 * method is the order in which the constants are declared.
166 */
167 public final int compareTo(E o) {
168 Enum other = (Enum)o;
169 Enum self = this;
170 if (self.getClass() != other.getClass() && // optimization
171 self.getDeclaringClass() != other.getDeclaringClass())
172 throw new ClassCastException();
173 return self.ordinal - other.ordinal;
174 }
175
176 /**
177 * Returns the Class object corresponding to this enum constant's
178 * enum type. Two enum constants e1 and e2 are of the
179 * same enum type if and only if
180 * e1.getDeclaringClass() == e2.getDeclaringClass().
181 * (The value returned by this method may differ from the one returned
182 * by the {@link Object#getClass} method for enum constants with
183 * constant-specific class bodies.)
184 *
185 * @return the Class object corresponding to this enum constant's
186 * enum type
187 */
188 public final Class<E> getDeclaringClass() {
189 Class clazz = getClass();
190 Class zuper = clazz.getSuperclass();
191 return (zuper == Enum.class) ? clazz : zuper;
192 }
193
194 /**
195 * Returns the enum constant of the specified enum type with the
196 * specified name. The name must match exactly an identifier used
197 * to declare an enum constant in this type. (Extraneous whitespace
198 * characters are not permitted.)
199 *
200 * @param enumType the {@code Class} object of the enum type from which
201 * to return a constant
202 * @param name the name of the constant to return
203 * @return the enum constant of the specified enum type with the
204 * specified name
205 * @throws IllegalArgumentException if the specified enum type has
206 * no constant with the specified name, or the specified
207 * class object does not represent an enum type
208 * @throws NullPointerException if {@code enumType} or {@code name}
209 * is null
210 * @since 1.5
211 */
212 public static <T extends Enum<T>> T valueOf(Class<T> enumType,
213 String name) {
214 T result = enumType.enumConstantDirectory().get(name);
215 if (result != null)
216 return result;
217 if (name == null)
218 throw new NullPointerException("Name is null");
219 throw new IllegalArgumentException(
220 "No enum constant " + enumType.getCanonicalName() + "." + name);
221 }
222
223 /**
224 * enum classes cannot have finalize methods.
225 */
226 protected final void finalize() { }
227
228 /**
229 * prevent default deserialization
230 */
231 private void readObject(ObjectInputStream in) throws IOException,
232 ClassNotFoundException {
233 throw new InvalidObjectException("can't deserialize enum");
234 }
235
236 private void readObjectNoData() throws ObjectStreamException {
237 throw new InvalidObjectException("can't deserialize enum");
238 }
239 }