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    }