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/* 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;
}
}
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