libjava/classpath/java/lang/Enum.java

   1 /* Enum.java - Base class for all enums
   2    Copyright (C) 2004, 2005 Free Software Foundation
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38 package java.lang;
  39
  40 import java.io.Serializable;
  41 import java.lang.reflect.Field;
  42
  43 /**
  44  * This class represents a Java enumeration.  All enumerations are
  45  * subclasses of this class.
  46  *
  47  * @author Tom Tromey (tromey@redhat.com)
  48  * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
  49  * @since 1.5
  50  */
  51 public abstract class Enum<T extends Enum<T>>
  52   implements Comparable<T>, Serializable
  53 {
  54
  55   /**
  56    * For compatability with Sun's JDK
  57    */
  58   private static final long serialVersionUID = -4300926546619394005L;
  59
  60   /**
  61    * The name of this enum constant.
  62    */
  63   final String name;
  64
  65   /**
  66    * The number of this enum constant.  Each constant is given a number
  67    * which matches the order in which it was declared, starting with zero.
  68    */
  69   final int ordinal;
  70
  71   /**
  72    * This constructor is used by the compiler to create enumeration constants.
  73    *
  74    * @param name the name of the enumeration constant.
  75    * @param ordinal the number of the enumeration constant, based on the
  76    *                declaration order of the constants and starting from zero.
  77    */
  78   protected Enum(String name, int ordinal)
  79   {
  80     this.name = name;
  81     this.ordinal = ordinal;
  82   }
  83
  84   /**
  85    * Returns an Enum for a enum class given a description string of
  86    * the enum constant.
  87    *
  88    * @exception NullPointerException when etype or s are null.
  89    * @exception IllegalArgumentException when there is no value s in
  90    * the enum etype.
  91    */
  92   public static <S extends Enum<S>> S valueOf(Class<S> etype, String s)
  93   {
  94     if (etype == null || s == null)
  95       throw new NullPointerException();
  96
  97     try
  98       {
  99         // 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 }