/*
Wotonomy: OpenStep design patterns for pure Java applications.
Copyright (C) 2000 Intersect Software Corporation

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, see http://www.gnu.org
*/

package net.wotonomy.control;

import java.util.Observable;
import java.util.Observer;

/**
* This is an abstract class for receiving coalesced
* notifications of changes from objects.
* This class also implements Observer for greater
* compatibility.
* The point of EODelayedObservers is that when
* they receive a willChange message, they
* queue themselves with a EODelayedObserverQueue
* so they can receive a single subjectChanged()
* after all changes from an observed object take
* place.
*
* @author michael@mpowers.net
* @author $Author: cgruber $
* @version $Revision: 894 $
*/
public abstract class EODelayedObserver
    implements EOObserving, Observer
{
    /**
    * Notified immediately.
    */
    public static final int ObserverPriorityImmediate = 0;
    public static final int ObserverPriorityFirst = 1;
    public static final int ObserverPrioritySecond = 2;
    public static final int ObserverPriorityThird = 3;
    public static final int ObserverPriorityFourth = 4;
    public static final int ObserverPriorityFifth = 5;
    public static final int ObserverPrioritySixth = 6;
    public static final int ObserverPriorityLater = 7;
    public static final int ObserverNumberOfPriorities = 8;
	
 	/**
	* Default constructor.  
	*/
	public EODelayedObserver ()
    {
    }

    /**
    * Removes this observer from the observer queue
    * for a currently pending notification.
    */
    public void discardPendingNotification ()
    {
        observerQueue().dequeueObserver( this );
    }

    /**
    * Returns the observer queue to which this observer
    * belongs.  This implementation returns the default
	* EODelayedObserverQueue.  
	* Override to use a different one.
    */
    public EODelayedObserverQueue observerQueue ()
    {
		return EODelayedObserverQueue.defaultObserverQueue();	
    }

    /**
    * Returns the priority of this observer in the queue.
	* This implementation returns ObserverPriorityThird.
	* Override to be notified before other observers.
    */
    public int priority ()
    {
        return ObserverPriorityThird;
    }

    /**
    * Notifies observer that one or more objects that
    * it is observing have changed.  The observer should
    * check all objects it is observing for changes.
    */
    public abstract void subjectChanged ();
    
    // interface EOObserving

    /**
    * Called when the specified object is about to change.
    * This implementation puts this observer on a 
    * notification queue.
    */
    public void objectWillChange ( Object anObject )
    {
        observerQueue().enqueueObserver( this );
    }
    
    // interface Observer
    
    /**
    * Called when the specified object has changed,
    * with the specified argument.
	* This method is included for interacting with
	* the java.lang.Observer pattern.
	* This implementation simply objectWillChange(anObject)
	* so that the observer still gets a single subjectChanged
	* call in response to multiple changes.
    */
    public void update ( Observable anObject, Object aValue )
    {
        objectWillChange( anObject );
    }

}

/*
 * $Log$
 * Revision 1.2  2006/02/16 16:47:14  cgruber
 * Move some classes in to "internal" packages and re-work imports, etc.
 *
 * Also use UnsupportedOperationExceptions where appropriate, instead of WotonomyExceptions.
 *
 * Revision 1.1  2006/02/16 13:19:57  cgruber
 * Check in all sources in eclipse-friendly maven-enabled packages.
 *
 * Revision 1.2  2001/10/26 18:38:10  mpowers
 * Reordered priorities.
 *
 * Revision 1.1.1.1  2000/12/21 15:46:38  mpowers
 * Contributing wotonomy.
 *
 * Revision 1.3  2000/12/20 16:25:35  michael
 * Added log to all files.
 *
 *
 */