三个线程模拟售票过程

superboboge 2014-09-26 12:34:54

代码：票类

public class Ticket {

	private int ticketNum = 100;

	public synchronized void sellTicket() {

		ticketNum --;

	}

	public synchronized int getTicketNum() {

		return ticketNum;

	}

	

}

买票类：

public class BuyTicket implements Runnable {

	private Ticket ticket;

	

	public void setTicket(Ticket ticket) {

		this.ticket = ticket;

	}



	@Override

	public void run() {

		while(ticket.getTicketNum()>0){

			ticket.sellTicket();

		System.out.println(Thread.currentThread().getName() + "卖了一张票剩余"+ticket.getTicketNum()+"张票" );



		}

	}



}

public class Main {

	public static void main(String[] args) throws InterruptedException {

		Ticket ticket = new Ticket();

		BuyTicket buyTicket = new BuyTicket();

		buyTicket.setTicket(ticket);

		Thread Thread1 = new Thread(buyTicket,"窗口1");

		Thread Thread2 = new Thread(buyTicket,"窗口2");

		Thread Thread3 = new Thread(buyTicket,"窗口3");

		Thread1.start();

		Thread2.start();

		Thread3.start();

	}

	

}

运行结果第一次售票总是会有剩下两个98张大家看看什么原因

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lliiqiang 2014-09-30

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这样肯定会有问题. 虽然买票过程同步了，但是获取票数信息的时候却和之前买票过程不同步，这个过程中会有其它线程改变票数，这个时候你得到的不是及时的你买完票之后的票数. public synchronized void sellTicket() { ticketNum --; System.out.println(Thread.currentThread().getName() + "卖了一张票剩余"+ticketNum+"张票" );//直接在买票方法里及时显示票数信息即可. }

dzq584462393 2014-09-29

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看了下出错的原因,第一个线程卖票(减一个),卖票的过程确实别的进程进不来,但是你卖完后,你还等着输出剩余多少票的时候,下一个进程就又卖票了,然后你在输入,所以发生2张票同时卖出的效果

wopabe 2014-09-29

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卖票过程没有错误，只是打印出来的信息欺骗了你，也就是说打印的不是卖的。你这样改下：先改下卖票方法

public synchronized int sellTicket() {
        ticketNum --;
        return ticketNum;
    }

然后改下run方法

while(ticket.getTicketNum()>0){
        System.out.println(Thread.currentThread().getName() + "卖了一张票剩余"+ticket.sellTicket()+"张票" );
        }

这样应该就可以了。个人感觉查询票数的方法getTicketNum没必要定义为同步方法，因为在这个方法里没有修改ticketNum。

zhangzhizhenshuzu 2014-09-29

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。。楼主不好意思。。刚才的代码还是会有点问题，同步代码块没把获取票数加进去，导致有线程先获取票数判断通过，再去买票。。导致票数结果又-1，-2.

这次的代码是终极版本。。调了半小时。。没问题了。。请参考。



public class SellTiketDemo {



    public static void main(String[] args) {

	

	        Ticket ticket = new Ticket();

	        BuyTicket buyTicket = new BuyTicket();

	        buyTicket.setTicket(ticket);

	        new Thread(buyTicket,"窗口1").start();;

	        new Thread(buyTicket,"窗口2").start();;

	        new Thread(buyTicket,"窗口3").start();;

    }



}



 class Ticket {

    private int  ticketNum = 1000;



       public  void sellTicket() {

	    ticketNum--;

	   

    }

   

   

    public   int  getTicketNum() {

	     return ticketNum;

    }

}

 

 class BuyTicket implements Runnable {

     private Ticket ticket;

      

     public  void setTicket(Ticket ticket) {

         this.ticket = ticket;

     }

  

     @Override

     public  void run() {

	  while(true){					//线程开始执行之后，先进入循环，再执行同步代码。这样避免了数据读写不同步的现象。

			 synchronized (ticket) {

			   

			  if(ticket.getTicketNum()>0){

    			    	ticket.sellTicket();

    			    	System.out.println(Thread.currentThread().getName() + "卖了一张票剩余"+ticket.getTicketNum()+"张票" );

    			   }

			   else {

			       	break;

			   }

		}

	 } 

      }	   

 }

运行结果：

zhangzhizhenshuzu 2014-09-29

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刚才运行了下，虽然共享数据不会出错了，貌似多线程的效率没体现出来，。改了一下


public class SellTiketDemo {

    public static void main(String[] args) {
	
	        Ticket ticket = new Ticket();
	        BuyTicket buyTicket = new BuyTicket();
	        buyTicket.setTicket(ticket);
	        new Thread(buyTicket,"窗口1").start();;
	        new Thread(buyTicket,"窗口2").start();;
	        new Thread(buyTicket,"窗口3").start();;
    }

}

 class Ticket {
    private int ticketNum = 1000;
   Object lockObject=new Object();
 
   
       public  void sellTicket() {
	   synchronized (lockObject) {
	    ticketNum--;
	    System.out.println(Thread.currentThread().getName() + "卖了一张票剩余"+this.getTicketNum()+"张票" );
	}
	
        
    }
   
   
    public  int  getTicketNum() {
	synchronized (lockObject) {
	      return ticketNum;
	}
      
        
    }
     
}
 
 class BuyTicket implements Runnable {
     private Ticket ticket;
      
     public  void setTicket(Ticket ticket) {
         this.ticket = ticket;
     }
  
     @Override
     public  void run() {
	 
            while(ticket.getTicketNum()>0){
        	
             ticket.sellTicket();
  
            } 
         }
     
  
 }

zhangzhizhenshuzu 2014-09-29

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楼主卖票本身没问题。只是打印顺序有问题，你的锁只有在sellTicket()方法内才有效。你想想，当一个线程执行完该方法，你的锁已经打开，这时候其他线程也可以卖票了。但是你的打印语句是在卖票方法之后再执行。。所以当然可能会出现打印的结果不是你期望的。解决方法：将锁的位置加在线程实现代码里。打印语句直接放在卖票方法sellTicket（）里。

public class SellTiketDemo { public static void main(String[] args) { Ticket ticket = new Ticket(); BuyTicket buyTicket = new BuyTicket(); buyTicket.setTicket(ticket); Thread Thread1 = new Thread(buyTicket,"窗口1"); Thread Thread2 = new Thread(buyTicket,"窗口2"); Thread Thread3 = new Thread(buyTicket,"窗口3"); Thread1.start(); Thread2.start(); Thread3.start(); } } class Ticket { private int ticketNum = 1000; public void sellTicket() { ticketNum--; System.out.println(Thread.currentThread().getName() + "卖了一张票剩余"+this.getTicketNum()+"张票" ); } public int getTicketNum() { return ticketNum; } } class BuyTicket implements Runnable { private Ticket ticket; public void setTicket(Ticket ticket) { this.ticket = ticket; } @Override public synchronized void run() { while(ticket.getTicketNum()>0){ ticket.sellTicket(); } } }

人_生而伟大 2014-09-29

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你的run（）方法也得是原子性的

binbinxyz 2014-09-28

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在卖票和显示信息的过程中加上同步：

	while (ticket.getTicketNum() > 0) 
	{
		synchronized(ticket)
		{
			ticket.sellTicket();
			System.out.println(Thread.currentThread().getName()
					+ "卖了一张票，剩余" + ticket.getTicketNum() + "张票");
		}
	}