libjava/java/util/Observable.java

/* Copyright (C) 1998, 1999  Cygnus Solutions

   This file is part of libgcj.

This software is copyrighted work licensed under the terms of the
Libgcj License.  Please consult the file "LIBGCJ_LICENSE" for
details.  */

package java.util;
 
/**
 * @author Warren Levy <warrenl@cygnus.com>
 * @date September 2, 1998.
 */
/* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
 * "The Java Language Specification", ISBN 0-201-63451-1
 * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
 * Status:  Believed complete and correct.
 */
 
public class Observable
{
  /* tracks whether this object has changed */
  private boolean changed;

  /* list of the Observers registered as interested in this Observable */
  private Vector observerVec;

  /* TBD: This might be better implemented as an Observer[]
   * but that would mean writing more code rather than making use of
   * the existing Vector class (this also implies a larger text code
   * space in resulting executables).  The tradeoff is one of speed
   * (manipulating the Observer[] directly) vs. size/reuse.  In the future,
   * we may decide to make the tradeoff and reimplement with an Observer[].
   */

  public Observable()
  {
    changed = false;
    observerVec = new Vector();
  }

  public synchronized void addObserver(Observer obs)
  {
    // JDK 1.2 spec says not to add this if it is already there
    if (!observerVec.contains(obs))
      observerVec.addElement(obs);
  }

  protected synchronized void clearChanged()
  {
    changed = false;
  }

  public synchronized int countObservers()
  {
    return observerVec.size();
  }

  public synchronized void deleteObserver(Observer obs)
  {
    observerVec.removeElement(obs);
  }

  public synchronized void deleteObservers()
  {
    observerVec.removeAllElements();
  }

  public synchronized boolean hasChanged()
  {
    return changed;
  }

  public void notifyObservers()
  {
    notifyObservers(null);
  }

  public void notifyObservers(Object arg)
  {
    if (changed)
      {
	/* The JDK 1.2 spec states that though the order of notification
	 * is unspecified in subclasses, in Observable it is in the order
	 * of registration.
	 */
        for (int i = 0, numObs = observerVec.size(); i < numObs; i++)
          ((Observer) (observerVec.elementAt(i))).update(this, arg);
        changed = false;
      }
  }

  protected synchronized void setChanged()
  {
    changed = true;
  }
}