/*
* @(#)Observable.java 1.12 95/08/18 Chris Warth
*
* Copyright (c) 1994 Sun Microsystems, Inc. All Rights Reserved.
*
* Permission to use, copy, modify, and distribute this software
* and its documentation for NON-COMMERCIAL purposes and without
* fee is hereby granted provided that this copyright notice
* appears in all copies. Please refer to the file "copyright.html"
* for further important copyright and licensing information.
*
* SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
* THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
* TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
* PARTICULAR PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR
* ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
* DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
*/
package java.util;
/*
* This class is used to hold the set of observers of an observable
* object whenever there is more than one observer.
*/
class ObserverList extends Vector {
/**
* Notifies all the observers in the list. This goes from
* back to front, so that it is OK to remove Observers from
* the list as a result of this call.
* @param who the list of observers
* @param arg what is being notified
*/
public void notifyObservers(Observable who, Object arg) {
int i = size();
while (--i >= 0) {
Observer o;
o = (Observer) elementAt(i);
o.update(who, arg);
}
}
}
/**
* This class should be subclassed by observable objetc, or "data"
* in the Model-View paradigm. An Observable object may have any
* number of Observers. Whenever the Observable instance changes, it
* notifies all of its observers. Notification is done by calling
* the update() method on all observers.
*
* @version 1.12, 18 Aug 1995
* @author Chris Warth
*/
public class Observable {
private boolean changed = false;
private Object obs;
/**
* Adds an observer to the observer list.
* @param o the observer to be added
*/
public synchronized void addObserver(Observer o) {
if (obs != null) {
if (obs instanceof ObserverList) {
if (!((ObserverList) obs).contains(o)) {
((ObserverList) obs).addElement(o);
}
} else if (obs != o) {
ObserverList tmp = new ObserverList();
tmp.addElement(obs);
tmp.addElement(o);
obs = tmp;
}
} else {
obs = o;
}
}
/**
* Deletes an observer from the observer list.
* @param o the observer to be deleted
*/
public synchronized void deleteObserver(Observer o) {
if (obs == o) {
obs = null;
} else if (obs != null && obs instanceof ObserverList) {
((ObserverList) obs).removeElement(o);
}
}
/**
* Notifies all observers if an observable change occurs.
*/
public void notifyObservers() {
notifyObservers(null);
}
/**
* Notifies all observers of the specified observable change
* which occurred.
* @param arg what is being notified
*/
public synchronized void notifyObservers(Object arg) {
if (hasChanged()) {
if (obs != null) {
if (obs instanceof ObserverList) {
((ObserverList) obs).notifyObservers(this, arg);
} else {
((Observer) obs).update(this, arg);
}
}
clearChanged();
}
}
/**
* Deletes observers from the observer list.
*/
public synchronized void deleteObservers() {
obs = null;
}
/**
* Sets a flag to note an observable change.
*/
protected synchronized void setChanged() {
changed = true;
}
/**
* Clears an observable change.
*/
protected synchronized void clearChanged() {
changed = false;
}
/**
* Returns a true boolean if an observable change has occurred.
*/
public synchronized boolean hasChanged() {
return changed;
}
/**
* Counts the number of observers.
*/
public synchronized int countObservers() {
if (obs != null) {
if (obs instanceof ObserverList) {
return ((ObserverList)obs).size();
} else {
return 1;
}
}
return 0;
}
}