libjava/gnu/java/io/ObjectIdentityWrapper.java

   1 /* ObjectIdentityWrapper.java -- Wrapper class used to override equals()
   2     and hashCode() to be as discriminating as possible
   3    Copyright (C) 1998 Free Software Foundation, Inc.
   4
   5 This file is part of GNU Classpath.
   6
   7 GNU Classpath is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2, or (at your option)
  10 any later version.
  11
  12 GNU Classpath is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15 General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU Classpath; see the file COPYING.  If not, write to the
  19 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  20 02111-1307 USA.
  21
  22 Linking this library statically or dynamically with other modules is
  23 making a combined work based on this library.  Thus, the terms and
  24 conditions of the GNU General Public License cover the whole
  25 combination.
  26
  27 As a special exception, the copyright holders of this library give you
  28 permission to link this library with independent modules to produce an
  29 executable, regardless of the license terms of these independent
  30 modules, and to copy and distribute the resulting executable under
  31 terms of your choice, provided that you also meet, for each linked
  32 independent module, the terms and conditions of the license of that
  33 module.  An independent module is a module which is not derived from
  34 or based on this library.  If you modify this library, you may extend
  35 this exception to your version of the library, but you are not
  36 obligated to do so.  If you do not wish to do so, delete this
  37 exception statement from your version. */
  38
  39
  40 package gnu.java.io;
  41
  42 /**
  43    This class is a thin wrapper around <code>Object</code> that makes
  44    the methods <code>hashCode()</code> and <code>equals(Object)</code>
  45    as discriminating as possible.
  46 */
  47 public class ObjectIdentityWrapper
  48 {
  49
  50   /**
  51      Constructs a <code>ObjectIdentityWrapper</code> that is wrapped
  52      around o.
  53   */
  54   public ObjectIdentityWrapper( Object o )
  55   {
  56     object = o;
  57   }
  58
  59   /**
  60      Uses <code>System.identityHashCode(Object)</code> to compute a
  61      hash code for the object wrapped by this
  62      <code>ObjectIdentityWrapper</code>.
  63
  64      @see java.lang.System#identityHashCode(java.lang.Object)
  65      @see java.util.Hashtable
  66      @see java.lang.Object#hashCode()
  67   */
  68   public int hashCode()
  69   {
  70     return System.identityHashCode( object );
  71   }
  72
  73   /**
  74      Uses the <code>==</code> operator to test for equality between
  75      the object wrapped by this <code>ObjectIdentityWrapper</code> and
  76      the object wrapped by the <code>ObjectIdentityWrapper</code> o.
  77      Returns false if o is not a <code>ObjectIdentityWrapper</code>.
  78
  79      @see java.util.Hashtable
  80      @see java.lang.Object#equals()
  81   */
  82   public boolean equals( Object o )
  83   {
  84     if( o instanceof ObjectIdentityWrapper )
  85       return object == ((ObjectIdentityWrapper)o).object;
  86     else
  87       return false;
  88   }
  89
  90   public String toString()
  91   {
  92     return "ObjectIdentityWrapper< " + object + ", " + hashCode() + " >";
  93   }
  94
  95   /**
  96      The <code>Object</code> wrapped by this
  97      <code>ObjectIdentityWrapper</code>.
  98   */
  99   public Object object;
 100 }