Source for gnu.classpath.jdwp.id.NullObjectId

   1: /* NullObjectId.java -- special objectId for null values
   2:    Copyright (C) 2007 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 gnu.classpath.jdwp.id;
  39: 
  40: import gnu.classpath.jdwp.exception.InvalidObjectException;
  41: import gnu.classpath.jdwp.util.NullObject;
  42: 
  43: import java.lang.ref.SoftReference;
  44: 
  45: /**
  46:  * This is a special case of an ObjectId.  When a varaible slot contains
  47:  * null as its value, this is a valid value despite the fact that it does
  48:  * not reference an object.  To represent this, this will always be the id
  49:  * of the NullObject (0).
  50:  *
  51:  * @author Kyle Galloway  <kgallowa@redhat.com>
  52:  */
  53: public class NullObjectId
  54:   extends ObjectId
  55: {
  56:   /**
  57:    * The object class that this id represents
  58:    */
  59:   public static final Class typeClass = NullObject.class;
  60: 
  61:   /**
  62:    * Constructs a new <code>NullObjectId</code>
  63:    */
  64:   public NullObjectId()
  65:   {
  66:     super();
  67:     setId((long) 0);
  68:     _reference = new SoftReference<NullObject>(new NullObject());
  69:     try
  70:       {
  71:         disableCollection();
  72:       }
  73:     catch(InvalidObjectException ex)
  74:       {
  75:         //This will not happen
  76:       }
  77:   }
  78: 
  79: }