/*
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.
 *
 *
 */