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 descriptions of the
38 * implicitly declared methods synthesized by the compiler, can be
39 * found in <i>The Java™ Language Specification, Third
40 * Edition</i>, <a
41 * href="http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.9">§8.9</a>.
42 *
43 * @param <E> The enum type subclass
44 * @author Josh Bloch
45 * @author Neal Gafter
46 * @see Class#getEnumConstants()
47 * @since 1.5
48 */
49 public abstract class Enum<E extends Enum<E>>
50 implements Comparable<E>, Serializable {
51 /**
52 * The name of this enum constant, as declared in the enum declaration.
53 * Most programmers should use the {@link #toString} method rather than
54 * accessing this field.
55 */
56 private final String name;
57
58 /**
59 * Returns the name of this enum constant, exactly as declared in its
60 * enum declaration.
61 *
62 * <b>Most programmers should use the {@link #toString} method in
63 * preference to this one, as the toString method may return
64 * a more user-friendly name.</b> This method is designed primarily for
65 * use in specialized situations where correctness depends on getting the
66 * exact name, which will not vary from release to release.
67 *
68 * @return the name of this enum constant
69 */
70 public final String name() {
71 return name;
72 }
73
74 /**
75 * The ordinal of this enumeration constant (its position
76 * in the enum declaration, where the initial constant is assigned
77 * an ordinal of zero).
78 *
79 * Most programmers will have no use for this field. It is designed
80 * for use by sophisticated enum-based data structures, such as
81 * {@link java.util.EnumSet} and {@link java.util.EnumMap}.
82 */
83 private final int ordinal;
84
85 /**
86 * Returns the ordinal of this enumeration constant (its position
87 * in its enum declaration, where the initial constant is assigned
88 * an ordinal of zero).
89 *
90 * Most programmers will have no use for this method. It is
91 * designed for use by sophisticated enum-based data structures, such
92 * as {@link java.util.EnumSet} and {@link java.util.EnumMap}.
93 *
94 * @return the ordinal of this enumeration constant
95 */
96 public final int ordinal() {
97 return ordinal;
98 }
99
100 /**
101 * Sole constructor. Programmers cannot invoke this constructor.
102 * It is for use by code emitted by the compiler in response to
103 * enum type declarations.
104 *
105 * @param name - The name of this enum constant, which is the identifier
106 * used to declare it.
107 * @param ordinal - The ordinal of this enumeration constant (its position
108 * in the enum declaration, where the initial constant is assigned
109 * an ordinal of zero).
110 */
111 protected Enum(String name, int ordinal) {
112 this.name = name;
113 this.ordinal = ordinal;
114 }
115
116 /**
117 * Returns the name of this enum constant, as contained in the
118 * declaration. This method may be overridden, though it typically
119 * isn't necessary or desirable. An enum type should override this
120 * method when a more "programmer-friendly" string form exists.
121 *
122 * @return the name of this enum constant
123 */
124 public String toString() {
125 return name;
126 }
127
128 /**
129 * Returns true if the specified object is equal to this
130 * enum constant.
131 *
132 * @param other the object to be compared for equality with this object.
133 * @return true if the specified object is equal to this
134 * enum constant.
135 */
136 public final boolean equals(Object other) {
137 return this==other;
138 }
139
140 /**
141 * Returns a hash code for this enum constant.
142 *
143 * @return a hash code for this enum constant.
144 */
145 public final int hashCode() {
146 return super.hashCode();
147 }
148
149 /**
150 * Throws CloneNotSupportedException. This guarantees that enums
151 * are never cloned, which is necessary to preserve their "singleton"
152 * status.
153 *
154 * @return (never returns)
155 */
156 protected final Object clone() throws CloneNotSupportedException {
157 throw new CloneNotSupportedException();
158 }
159
160 /**
161 * Compares this enum with the specified object for order. Returns a
162 * negative integer, zero, or a positive integer as this object is less
163 * than, equal to, or greater than the specified object.
164 *
165 * Enum constants are only comparable to other enum constants of the
166 * same enum type. The natural order implemented by this
167 * method is the order in which the constants are declared.
168 */
169 public final int compareTo(E o) {
170 Enum other = (Enum)o;
171 Enum self = this;
172 if (self.getClass() != other.getClass() && // optimization
173 self.getDeclaringClass() != other.getDeclaringClass())
174 throw new ClassCastException();
175 return self.ordinal - other.ordinal;
176 }
177
178 /**
179 * Returns the Class object corresponding to this enum constant's
180 * enum type. Two enum constants e1 and e2 are of the
181 * same enum type if and only if
182 * e1.getDeclaringClass() == e2.getDeclaringClass().
183 * (The value returned by this method may differ from the one returned
184 * by the {@link Object#getClass} method for enum constants with
185 * constant-specific class bodies.)
186 *
187 * @return the Class object corresponding to this enum constant's
188 * enum type
189 */
190 public final Class<E> getDeclaringClass() {
191 Class clazz = getClass();
192 Class zuper = clazz.getSuperclass();
193 return (zuper == Enum.class) ? clazz : zuper;
194 }
195
196 /**
197 * Returns the enum constant of the specified enum type with the
198 * specified name. The name must match exactly an identifier used
199 * to declare an enum constant in this type. (Extraneous whitespace
200 * characters are not permitted.)
201 *
202 * <p>Note that for a particular enum type {@code T}, the
203 * implicitly declared {@code public static T valueOf(String)}
204 * method on that enum may be used instead of this method to map
205 * from a name to the corresponding enum constant. All the
206 * constants of an enum type can be obtained by calling the
207 * implicit {@code public static T[] values()} method of that
208 * type.
209 *
210 * @param <T> The enum type whose constant is to be returned
211 * @param enumType the {@code Class} object of the enum type from which
212 * to return a constant
213 * @param name the name of the constant to return
214 * @return the enum constant of the specified enum type with the
215 * specified name
216 * @throws IllegalArgumentException if the specified enum type has
217 * no constant with the specified name, or the specified
218 * class object does not represent an enum type
219 * @throws NullPointerException if {@code enumType} or {@code name}
220 * is null
221 * @since 1.5
222 */
223 public static <T extends Enum<T>> T valueOf(Class<T> enumType,
224 String name) {
225 T result = enumType.enumConstantDirectory().get(name);
226 if (result != null)
227 return result;
228 if (name == null)
229 throw new NullPointerException("Name is null");
230 throw new IllegalArgumentException(
231 "No enum constant " + enumType.getCanonicalName() + "." + name);
232 }
233
234 /**
235 * enum classes cannot have finalize methods.
236 */
237 protected final void finalize() { }
238
239 /**
240 * prevent default deserialization
241 */
242 private void readObject(ObjectInputStream in) throws IOException,
243 ClassNotFoundException {
244 throw new InvalidObjectException("can't deserialize enum");
245 }
246
247 private void readObjectNoData() throws ObjectStreamException {
248 throw new InvalidObjectException("can't deserialize enum");
249 }
250 }