dataeventobservable.java

自己写的一个聊天的小程序 请多多指教

/*
 * Copyright (c) 2003 - 2007, Silvio Meier and Tobias Reinhard
 *
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, 
 * with or without modification, are permitted provided 
 * that the following conditions are met:
 *
 *   o Redistributions of source code must retain the above 
 *     copyright notice, this list of conditions and the 
 *     following disclaimer.
 *   o Redistributions in binary form must reproduce the above 
 *     copyright notice, this list of conditions and the 
 *     following disclaimer in the documentation and/or other 
 *     materials provided with the distribution.
 *   o The names of its contributors may not be used to endorse 
 *     or promote products derived from this software without 
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package net.sf.cscc;

import java.util.Enumeration;
import java.util.Vector;

/**
 *  This class provides the functionality for observing the incoming
 *  data event queue of the communication system.
 *
 *	@author             Silvio Meier (SM)
 *	@copyright          Silvio Meier, Tobias Reinhard, 2003
 *	@history            2003-05-09 SM First Version
 *                      2003-05-14 SM working on additional methods and events,
 *                                    correction of some comments.
 *                      2003-05-20 TR Comments corrected
 *                      2006-11-02 SM Comments revised.
 *	@version            $Date: 2007/07/01 17:04:06 $, $Author: reode_orm $, $Revision: 1.1 $
 */
class DataEventObservable {

    /**
     * Contains a list of objects implementing the {@link net.sf.cscc.DataEventObserver}
     * or the {@link net.sf.cscc.DataEventReceivingObserver} interface.
     */
    private Vector observers;

    /**
     *   This constructor initializes the observable object.
     *
     *   @pre true
     *   @post observers != null
     */
    public DataEventObservable() {
        observers = new Vector();
    }

    /**
     *   Removes a given observer from the list of data event observers.
     *   If the given observer is not in the observer list, nothing happens.
     *
     *   @pre o != null
     *   @post ((observers.size())@pre == (observers.size())@post + 1 &&
     *          (obervers.contains(o))@pre) || (!(observers.contains(o))
     *   @param o Observer which should be eliminated from the observer list.
     */
    public synchronized  void removeDataEventObserver(DataEventBaseObserver o) {
        observers.remove(o);
    }


    /**
     *   Notifies all observers in the observer list by sending them the given
     *   data event. The observers have to implement either the
     *   {@link net.sf.cscc.DataEventReceivingObserver}
     *   or the {@link net.sf.cscc.DataEventObserver} interface.
     *   If the observer does only implement the super interface
     *   {@link net.sf.cscc.DataEventBaseObserver}, no event is
     *   propagated to the observer.
     *
     *   @pre de != null
     *   @post true
     *   @param de DataEvent object which is sent to the observers.
     *   @return Returns true after the delivery of the data event to
     *           all observers, ie. all the observers got the event data.
     *           Afterwards, the delivered event is ready to be removed
     *           from the queue.
     */
    public synchronized  boolean notifyDataEventObservers(DataEvent de) {
        boolean dequeue = true;
        Enumeration e = observers.elements();
        while (e.hasMoreElements()) {
            Object o = e.nextElement();
            if (o instanceof DataEventObserver) {
                ((DataEventObserver)o).receiveEvent();
                dequeue = false;
            }
            else {
                if (o instanceof DataEventReceivingObserver) {
                    ((DataEventReceivingObserver)o).receiveEvent(de);
                }
            }
        }
        return dequeue;
    }

    /**
     *   Adds an oberver to the observer list. In the case the observer is
     *   already in the list, it is added again, so
     *   that multiple event notifications can happen. The observer may not
     *   be null!
     *
     *   @pre  o != null
     *   @post ((observers.size())@pre == (observers.size())@post - 1
     *   @param o Observer to add to the list
     */
    public synchronized void addDataObserver(DataEventBaseObserver o) {
        observers.add(o);
    }
}