/*
 * @(#) Notifiable.java - Interface for custom observer agents.
 * (c) 2000 Ivan Maidanski <ivmai@chat.ru> http://ivmai.chat.ru
 * Freeware class library sources. All rights reserved.
 **
 * Language: Java [pure]
 * Tested with: JDK v1.1.6
 * Last modified: 2000-12-25 10:15:00 GMT+03:00
 */

/*
 * This software is the proprietary information of the author.
 **
 * Permission to use, copy, 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.
 **
 * This software should not be modified in any way; any found bug
 * should be reported to the author.
 **
 * The author disclaims all warranties with regard to this software,
 * including all implied warranties of merchantability and fitness.
 * In no event shall the author be liable for any special, indirect
 * or consequential damages or any damages whatsoever resulting from
 * loss of use, data or profits, whether in an action of contract,
 * negligence or other tortuous action, arising out of or in
 * connection with the use or performance of this software.
 */

package ivmai.util;

/**
 * Interface for custom observer agents.
 **
 * A class should implement (or should have a private class which
 * implements) this interface when it wants to be informed of
 * changes in the observable object. Normally, observer agent serves
 * as an intermediate entity between one or more observed entities
 * and the application entity which wants to be notified (with
 * details) only on the events in these observed objects.
 * <CODE>Verifiable</CODE> interface is extended to allow integrity
 * checking for typical agent objects. Important notes: agents must
 * not modify <VAR>observed</VAR> object anyhow; notification should
 * be performed just after changes; this notification mechanism has
 * nothing to do with threads and is completely separate from the
 * 'wait-notify' mechanism of <CODE>Object</CODE>. Here is the usage
 * example of an observer agent:
 **
 * <CODE><PRE>
 * final class MyAgent // hidden helper class
 * implements Notifiable
 * {
 * private final MyClass myClass; // myClass != null
 * protected MyAgent(MyClass myClass)
 * throws NullPointerException
 * {
 * myClass.equals(myClass);
 * this.myClass = myClass;
 * }
 * public void update(MultiObservable observed, Object argument)
 * {
 * MyClass myClass = this.myClass;
 * if (argument instanceof MyEvent && myClass.observed == observed)
 * // safe (private) actions on myClass
 * }
 * public void integrityCheck()
 * {
 * if (myClass == null)
 * throw new InternalError("myClass: null");
 * }
 * }
 * private transient Notifiable agent = new MyAgent(this);
 * . . .
 * observed.addObserver(agent);
 * . . .
 * observed.removeObserver(agent); // stop observing
 * </PRE></CODE>
 **
 * @see MultiObservable
 **
 * @version 2.0
 * @author Ivan Maidanski
 */
public interface Notifiable extends Verifiable
{

/**
 * Notifies <CODE>this</CODE> observer agent on a particular event
 * that just occurred.
 **
 * This method is called whenever <VAR>observed</VAR> object is
 * changed. Important notes: <VAR>observed</VAR> object should not
 * be modified during the notification; types of <VAR>observed</VAR>
 * and <VAR>argument</VAR> should be checked inside; no access
 * should be provided to the instance of this interface (since this
 * method is <CODE>public</CODE>) outside hidden
 * <CODE>notifyObservers</CODE> method of <VAR>observed</VAR>
 * object; <CODE>RuntimeException</CODE> (and
 * <CODE>OutOfMemoryError</CODE>) may be thrown if a notification
 * failure has occurred.
 **
 * @param observed
 * the observed object (may be <CODE>null</CODE>, should be checked
 * inside).
 * @param argument
 * the argument (may be <CODE>null</CODE>, should be checked inside)
 * describing the occurred event.
 * @exception RuntimeException
 * if the notification process has failed (a custom exception).
 * @exception OutOfMemoryError
 * if there is not enough memory (to perform notification).
 */
 public abstract void update(MultiObservable observed,
         Object argument);
}