onetimequeue.java

ALGAE是一个快速创建算法演示的框架。目前支持的算法实现语言包括java和c

package edu.odu.cs.zeil.AlgAE.Server;

import edu.odu.cs.zeil.AlgAE.Server.TimeStamped;
/**
 * A queue of time-stamped objects, used to provide queue-like
 * behavior with the provision that any object currently or
 * previously in the queue, cannot enter the queue a second time.
 *
 * @author Steven J. Zeil
 * @version
 */

public class OneTimeQueue {

  class QueueNode 
  {
    TimeStamped data;
    QueueNode next;

    QueueNode (TimeStamped o) {data = o; next = null;}
  }

  private QueueNode front;
  private QueueNode rear;
  private int theSize;
  private static int theStamp = 0;
  private static Boolean lock = new Boolean (false);
  
    
  public OneTimeQueue() {
    front = null;
    rear = null;
    theSize = 0;
    synchronized (lock)
      {
	++theStamp;
      }
  }

  public TimeStamped getFront()
  {
    return front.data;
  }

  public void removeFront()
  {
    if (front != null) {
      front = front.next;
      if (front == null) {
	rear = null;
      }
      --theSize;
    }
  }

  public void addToRear(TimeStamped newElement)
  {
    if (newElement.getStamp() < theStamp)
	{
	    QueueNode qn = new QueueNode (newElement);
	    if (front == null) {
		front = qn;
		rear = qn;
	    }
	    else {
		rear.next = qn;
		rear = qn;
	    }
	    ++theSize;
	    newElement.putStamp(theStamp);
	}
  }


  public int size()
  {
    return theSize;
  }

  public boolean isEmpty()
  {
    return (theSize == 0);
  }
  
}