java线程技术3_线程的同步

      Thread类中的join方法的功能就是使异步执行的线程变成同步执行。
      thread.join()应该是让其它线程进入阻塞状态，等当前的thread执行完之后，才允许其它线程执行 。
例：

/**
 * 线程的join举例.
 * @version V1.0 ,2011-4-1
 * @author xiahui
 */
public class JoinThread extends Thread
{
     private int count=0;

    public void run(){
        while (true){
          System.out.println(this.getName()+(++count));
          try{
            sleep(300);
          }catch(InterruptedException ex){
          }
          if(count == 3)
            return;
        }
      }

    public static void main(String[] args) throws Exception
    {
        JoinThread counter1= new JoinThread();
        JoinThread counter2 = new JoinThread();
        JoinThread counter3 = new JoinThread();

        counter1.setName("counter1_");
        counter2.setName("counter2_");
        counter3.setName("counter3_");

        counter1.start();
        counter2.start();
        counter3.start();
    }

}

输出结果

counter1_1
counter3_1
counter2_1
counter1_2
counter3_2
counter2_2
counter1_3
counter2_3
counter3_3

从结果可以看出，三个线程是异步执行的，输出的次序是无序的

现在要求三个线程依次执行

        counter1.start();
        counter1.join(); //等待counter1结束，其它线程才能执行
        counter2.start();
        counter2.join();//等待counter2结束，其它线程才能执行
        counter3.start();

输出结果

counter1_1
counter1_2
counter1_3
counter2_1
counter2_2
counter2_3
counter3_1
counter3_2
counter3_3

参考文献
1.