queue.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.Vector;

/**
 *  This class is a thread safe event queue, ie. data events are stored
 *  in the order they occurred (FIFO).
 *
 *	@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
 *                      2003-06-13 SM Addtional method for querying size of the queue.
 * 						2004-12-13 SM Some cleaning of unused things.
 * 						2006-11-28 SM Revised comments.
 *	@version            $Date: 2007/07/01 17:04:05 $, $Author: reode_orm $, $Revision: 1.1 $
 */
class Queue {
    
    /**
     *	Used to store all the data events which recently occurred.
     */
    private Vector dataEvents;
    
    /**   
     * Creates the thread safe event queue and initializes the container
     * i.e. the Vector object in which the events are stored.
     * 
     * @pre true
     * @post dataEvents != null
     */
    public Queue() {
        dataEvents = new Vector();
    }
    
    /**
     *   Enqueues a new DataEvent object at the end of the event queue.
     *   
     *   @pre de != null
     *   @post (dataEvents.size())@pre == (dataEvents.size())@post + 1
     *   @param de DataEvent object which is enqued at the end of the queue.
     */
    public synchronized void enqueueDataEvent(DataEvent de) {
        dataEvents.add(de);
    }
    
    /**
     *   Returns the oldest event in the event queue and deletes it from
     *   the queue.
     *   
     *   @pre dataEvents.size() > 0
     *   @post (dataEvents.size())@pre == (dataEvents.size())@post - 1
     *   @return Returns the oldest DataEvent Element in the queue.
     */
    public synchronized  DataEvent dequeueDataEvent() {
        Object ret = dataEvents.elementAt(0);
        dataEvents.remove(0);
        return (DataEvent)ret;
    }
    
    /**
     *   This method returns the oldest element from the queue without removing
     *   it from the queue.
     *   
     *   @pre  dataEvents.size() > 0
     *   @post true
     *   @invariant (dataEvents.size())@pre == (dataEvents.size())@post
     *   @return Oldest DataEvent object from the queue.
     */
    public synchronized  DataEvent getDataEvent() {
        Object ret = dataEvents.elementAt(0);
        return (DataEvent) ret;
    }
    
    
    /**
     *   Removes the oldest DataEvent object from the queue.
     *   
     *   @pre dataEvents.size() > 0
     *   @post (dataEvents.size())@pre == (dataEvents.size())@post - 1
     */
    public synchronized  void removeDataEvent() {
        dataEvents.remove(0);
    }
    
    /**
     *   This method returns true, if there are DataEvents in the queue.
     *   This method can be used, if clients using the communication component
     *   implement a pull model instead of a push (observer) model.
     *   
     *   @pre true
     *   @post true
     *   @invariant(dataEvents.size())@pre == (dataEvents.size())@post
     *   
     *   @return Returns true, if there is at least one element in the
     *           queue.
     */
    public synchronized boolean hasDataEvents() {
        return (dataEvents.size() > 0);
    }
    
    /**
     *   This method returns the size of the queue.
     *   
     *   @pre true
     *   @post true
     *   
     *   @return Returns the number of elements in the queue. If no elements
     *           are in the queue, nothing is returned.
     */
    public synchronized int size() {
        return dataEvents.size();
    }
}