libjava/java/util/Observable.java

   1 /* Copyright (C) 1998, 1999  Red Hat, Inc.
   2
   3    This file is part of libgcj.
   4
   5 This software is copyrighted work licensed under the terms of the
   6 Libgcj License.  Please consult the file "LIBGCJ_LICENSE" for
   7 details.  */
   8
   9 package java.util;
  10
  11 /**
  12  * @author Warren Levy <warrenl@cygnus.com>
  13  * @date September 2, 1998.
  14  */
  15 /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
  16  * "The Java Language Specification", ISBN 0-201-63451-1
  17  * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
  18  * Status:  Believed complete and correct.
  19  */
  20
  21 public class Observable
  22 {
  23   /* tracks whether this object has changed */
  24   private boolean changed;
  25
  26   /* list of the Observers registered as interested in this Observable */
  27   private Vector observerVec;
  28
  29   /* TBD: This might be better implemented as an Observer[]
  30    * but that would mean writing more code rather than making use of
  31    * the existing Vector class (this also implies a larger text code
  32    * space in resulting executables).  The tradeoff is one of speed
  33    * (manipulating the Observer[] directly) vs. size/reuse.  In the future,
  34    * we may decide to make the tradeoff and reimplement with an Observer[].
  35    */
  36
  37   public Observable()
  38   {
  39     changed = false;
  40     observerVec = new Vector();
  41   }
  42
  43   public synchronized void addObserver(Observer obs)
  44   {
  45     // JDK 1.2 spec says not to add this if it is already there
  46     if (!observerVec.contains(obs))
  47       observerVec.addElement(obs);
  48   }
  49
  50   protected synchronized void clearChanged()
  51   {
  52     changed = false;
  53   }
  54
  55   public synchronized int countObservers()
  56   {
  57     return observerVec.size();
  58   }
  59
  60   public synchronized void deleteObserver(Observer obs)
  61   {
  62     observerVec.removeElement(obs);
  63   }
  64
  65   public synchronized void deleteObservers()
  66   {
  67     observerVec.removeAllElements();
  68   }
  69
  70   public synchronized boolean hasChanged()
  71   {
  72     return changed;
  73   }
  74
  75   public void notifyObservers()
  76   {
  77     notifyObservers(null);
  78   }
  79
  80   public void notifyObservers(Object arg)
  81   {
  82     if (changed)
  83       {
  84         /* The JDK 1.2 spec states that though the order of notification
  85          * is unspecified in subclasses, in Observable it is in the order
  86          * of registration.
  87          */
  88         for (int i = 0, numObs = observerVec.size(); i < numObs; i++)
  89           ((Observer) (observerVec.elementAt(i))).update(this, arg);
  90         changed = false;
  91       }
  92   }
  93
  94   protected synchronized void setChanged()
  95   {
  96     changed = true;
  97   }
  98 }