simplequeue.java

java 编写的程序

package source.org.apache.java.util;

/*
 * Copyright (c) 1997-1999 The Java Apache Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. 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.
 *
 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the Java Apache 
 *    Project for use in the Apache JServ servlet engine project
 *    <http://java.apache.org/>."
 *
 * 4. The names "Apache JServ", "Apache JServ Servlet Engine" and 
 *    "Java Apache Project" must not be used to endorse or promote products 
 *    derived from this software without prior written permission.
 *
 * 5. Products derived from this software may not be called "Apache JServ"
 *    nor may "Apache" nor "Apache JServ" appear in their names without 
 *    prior written permission of the Java Apache Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the Java Apache 
 *    Project for use in the Apache JServ servlet engine project
 *    <http://java.apache.org/>."
 *    
 * THIS SOFTWARE IS PROVIDED BY THE JAVA APACHE PROJECT "AS IS" AND ANY
 * EXPRESSED 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 JAVA APACHE PROJECT OR
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 * 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.
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Java Apache Group. For more information
 * on the Java Apache Project and the Apache JServ Servlet Engine project,
 * please see <http://java.apache.org/>.
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 */

import java.util.Vector;

/**
 * Implements single queue.
 * <p>
 *
 * Extremely simplified queue implementation, cut to fit into the background
 * logging.
 *
 * @author <a href="[e-mail]">Vadim Tkachenko</a>
 * @version $Revision: 1.2 $ $Date: 2000/08/08 14:01:44 $
 */
public class SimpleQueue {
	/**
	 * Data holder.
	 */
	private Vector theQueue;

	/**
	 * Default constructor.
	 */
	public SimpleQueue() {
		theQueue = new Vector();
	}
	/**
	 * Get the object waiting in the queue.
	 * Asynchronous.
	 * @return null if the queue is empty.
	 */
	public synchronized Object get() {
		Object  found = peekAtHead();
		if (found != null) {
			theQueue.removeElementAt(0);
		} else {
			return found;
		}

	return found;
	}
	/**
	 * Find out if the queue is empty.
	 */
	public boolean isEmpty() {
		return theQueue.isEmpty();
   }   
	/**
	 * Get the object at the head of the queue.
	 * @return null if the queue is empty.
	 */
	public synchronized Object peekAtHead() {
		if (theQueue.isEmpty()) {
			return null;
		}

		return theQueue.elementAt(0);
	}
	/**
	 * Put the object into the queue.
	 *
	 * @param toPut the object to put
	 */
	public synchronized void put(Object toPut) {
		theQueue.addElement(toPut);
		notify();
	}
   /**
	* Get the number of elements in the queue.
	*/
   public int size() {
	   return theQueue.size();
   }   
	/**
	 * Wait until the object appears in the queue, then return it.
	 * @return The object from the queue.
	 * @exception InterruptedException if this thread was interrupted by another thread.
	 * @see #get
	 */
	public synchronized Object waitObject() throws InterruptedException {
		while (isEmpty()) {
			wait();
		}
		return get();
	}
}