(轉(zhuǎn))Java中join和yield的作用

_小女子_ 2015-03-27

展開全文

原文：http://blog.csdn.net/reboot123/article/details/22589621
本文來自 http://blog.csdn.net/liuxian13183/ ，引用必須注明出處！
1、 A.join，在API中的解釋是，堵塞當(dāng)前線程B，直到A執(zhí)行完畢并死掉，再執(zhí)行B。

用一個小例子來說明吧

static class ThreadA extends Thread {
    @Override
    public void run() {
      // TODO Auto-generated method stub
      super.run();
      for (int i = 0; i < 10; i++) {
        System.out.println("ThreadA" + i);
      }
    }
  }

  static class ThreadB extends Thread {
    ThreadA a;

    public ThreadB(ThreadA a) {
      // TODO Auto-generated constructor stub
      this.a = a;
    }

    @Override
    public void run() {
      // TODO Auto-generated method stub
      super.run();
      System.out.println("ThreadB start");
      try {
        a.join();
      } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
      }
      System.out.println("ThreadB end");
    }
  }

  public static void main(String[] args) {
    ThreadA a = new ThreadA();
    ThreadB b = new ThreadB(a);
    b.start();
    a.start();
  }

執(zhí)行結(jié)果：

ThreadB start
ThreadA0
ThreadA1
ThreadA2
ThreadA3
ThreadA4
ThreadA5
ThreadA6
ThreadA7
ThreadA8
ThreadA9
ThreadB end

首先b線程執(zhí)行，a線程join后，直接執(zhí)行完a，然后才執(zhí)行b，證實上述說法。

2、A.yield，A讓出位置，給B執(zhí)行，B執(zhí)行結(jié)束A再執(zhí)行。跟join意思正好相反！

static class ThreadA extends Thread {
    @Override
    public void run() {
      // TODO Auto-generated method stub
      super.run();
      for (int i = 0; i < 10; i++) {
        System.out.println("ThreadA " + i);
      }
    }
  }

  static class ThreadB extends Thread {
    ThreadA a;

    public ThreadB(ThreadA a) {
      // TODO Auto-generated constructor stub
      this.a = a;
    }

    @Override
    public void run() {
      // TODO Auto-generated method stub
      super.run();
      System.out.println("ThreadB start");
      try {
        for (int i = 0; i < 10; i++) {
          if(i==2){
            a.yield();
          }
          System.out.println("ThreadB " + i);
        }
      } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
      }
      System.out.println("ThreadB end");
    }
  }

  public static void main(String[] args) {
    ThreadA a = new ThreadA();
    ThreadB b = new ThreadB(a);
    b.start();
    a.start();
  }

執(zhí)行結(jié)果：

ThreadB start
ThreadA 0
ThreadB 0
ThreadA 1
ThreadB 1
ThreadA 2
ThreadB 2
ThreadB 3
ThreadB 4
ThreadB 5
ThreadB 6
ThreadB 7
ThreadB 8
ThreadB 9
ThreadB end
ThreadA 3
ThreadA 4
ThreadA 5
ThreadA 6
ThreadA 7
ThreadA 8
ThreadA 9