001 /* Enum.java - Base class for all enums
002 Copyright (C) 2004, 2005 Free Software Foundation
003
004 This file is part of GNU Classpath.
005
006 GNU Classpath is free software; you can redistribute it and/or modify
007 it under the terms of the GNU General Public License as published by
008 the Free Software Foundation; either version 2, or (at your option)
009 any later version.
010
011 GNU Classpath is distributed in the hope that it will be useful, but
012 WITHOUT ANY WARRANTY; without even the implied warranty of
013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014 General Public License for more details.
015
016 You should have received a copy of the GNU General Public License
017 along with GNU Classpath; see the file COPYING. If not, write to the
018 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019 02110-1301 USA.
020
021 Linking this library statically or dynamically with other modules is
022 making a combined work based on this library. Thus, the terms and
023 conditions of the GNU General Public License cover the whole
024 combination.
025
026 As a special exception, the copyright holders of this library give you
027 permission to link this library with independent modules to produce an
028 executable, regardless of the license terms of these independent
029 modules, and to copy and distribute the resulting executable under
030 terms of your choice, provided that you also meet, for each linked
031 independent module, the terms and conditions of the license of that
032 module. An independent module is a module which is not derived from
033 or based on this library. If you modify this library, you may extend
034 this exception to your version of the library, but you are not
035 obligated to do so. If you do not wish to do so, delete this
036 exception statement from your version. */
037
038 package java.lang;
039
040 import java.io.Serializable;
041 import java.lang.reflect.Field;
042
043 /**
044 * This class represents a Java enumeration. All enumerations are
045 * subclasses of this class.
046 *
047 * @author Tom Tromey (tromey@redhat.com)
048 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
049 * @since 1.5
050 */
051 public abstract class Enum<T extends Enum<T>>
052 implements Comparable<T>, Serializable
053 {
054
055 /**
056 * For compatability with Sun's JDK
057 */
058 private static final long serialVersionUID = -4300926546619394005L;
059
060 /**
061 * The name of this enum constant.
062 */
063 final String name;
064
065 /**
066 * The number of this enum constant. Each constant is given a number
067 * which matches the order in which it was declared, starting with zero.
068 */
069 final int ordinal;
070
071 /**
072 * This constructor is used by the compiler to create enumeration constants.
073 *
074 * @param name the name of the enumeration constant.
075 * @param ordinal the number of the enumeration constant, based on the
076 * declaration order of the constants and starting from zero.
077 */
078 protected Enum(String name, int ordinal)
079 {
080 this.name = name;
081 this.ordinal = ordinal;
082 }
083
084 /**
085 * Returns an Enum for a enum class given a description string of
086 * the enum constant.
087 *
088 * @exception NullPointerException when etype or s are null.
089 * @exception IllegalArgumentException when there is no value s in
090 * the enum etype.
091 */
092 public static <S extends Enum<S>> S valueOf(Class<S> etype, String s)
093 {
094 if (etype == null || s == null)
095 throw new NullPointerException();
096
097 try
098 {
099 // XXX We should not use getDeclaredField, because it does
100 // an unnecessary security check.
101 Field f = etype.getDeclaredField(s);
102 if (! f.isEnumConstant())
103 throw new IllegalArgumentException(s);
104 Class.setAccessible(f);
105 @SuppressWarnings("unchecked")
106 S val = (S) f.get(null);
107 return val;
108 }
109 catch (NoSuchFieldException exception)
110 {
111 throw new IllegalArgumentException(s);
112 }
113 catch (IllegalAccessException exception)
114 {
115 throw new Error("Unable to access Enum class");
116 }
117 }
118
119 /**
120 * Returns true if this enumeration is equivalent to the supplied object,
121 * <code>o</code>. Only one instance of an enumeration constant exists,
122 * so the comparison is simply done using <code>==</code>.
123 *
124 * @param o the object to compare to this.
125 * @return true if <code>this == o</code>.
126 */
127 public final boolean equals(Object o)
128 {
129 // Enum constants are singular, so we need only compare `=='.
130 return this == o;
131 }
132
133 /**
134 * Returns the hash code of this constant. This is simply the ordinal.
135 *
136 * @return the hash code of this enumeration constant.
137 */
138 public final int hashCode()
139 {
140 return ordinal;
141 }
142
143 /**
144 * Returns a textual representation of this enumeration constant.
145 * By default, this is simply the declared name of the constant, but
146 * specific enumeration types may provide an implementation more suited
147 * to the data being stored.
148 *
149 * @return a textual representation of this constant.
150 */
151 public String toString()
152 {
153 return name;
154 }
155
156 /**
157 * Returns an integer which represents the relative ordering of this
158 * enumeration constant. Enumeration constants are ordered by their
159 * ordinals, which represents their declaration order. So, comparing
160 * two identical constants yields zero, while one declared prior to
161 * this returns a positive integer and one declared after yields a
162 * negative integer.
163 *
164 * @param e the enumeration constant to compare.
165 * @return a negative integer if <code>e.ordinal < this.ordinal</code>,
166 * zero if <code>e.ordinal == this.ordinal</code> and a positive
167 * integer if <code>e.ordinal > this.ordinal</code>.
168 * @throws ClassCastException if <code>e</code> is not an enumeration
169 * constant of the same class.
170 */
171 public final int compareTo(T e)
172 {
173 if (getDeclaringClass() != e.getDeclaringClass())
174 throw new ClassCastException();
175 return ordinal - e.ordinal;
176 }
177
178 /**
179 * Cloning of enumeration constants is prevented, to maintain their
180 * singleton status.
181 *
182 * @return the cloned object.
183 * @throws CloneNotSupportedException as enumeration constants can't be
184 * cloned.
185 */
186 protected final Object clone() throws CloneNotSupportedException
187 {
188 throw new CloneNotSupportedException("can't clone an enum constant");
189 }
190
191 /**
192 * Returns the name of this enumeration constant.
193 *
194 * @return the name of the constant.
195 */
196 public final String name()
197 {
198 return name;
199 }
200
201 /**
202 * Returns the number of this enumeration constant, which represents
203 * the order in which it was originally declared, starting from zero.
204 *
205 * @return the number of this constant.
206 */
207 public final int ordinal()
208 {
209 return ordinal;
210 }
211
212 /**
213 * Returns the type of this enumeration constant. This is the class
214 * corresponding to the declaration of the enumeration.
215 *
216 * @return the type of this enumeration constant.
217 */
218 public final Class<T> getDeclaringClass()
219 {
220 Class k = getClass();
221 // We might be in an anonymous subclass of the enum class, so go
222 // up one more level.
223 if (k.getSuperclass() != Enum.class)
224 k = k.getSuperclass();
225 return k;
226 }
227
228 /**
229 * Enumerations can not have finalization methods.
230 *
231 * @since 1.6
232 */
233 protected final void finalize()
234 {
235 }
236
237 }