Java中join和yield的作用

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本文来自http://blog.csdn.net/liuxian13183/ ，引用必须注明出处！

1、 A.join，在API中的解释是，堵塞当前线程B，直到A执行完毕并死掉，再执行B。

用一个小例子来说明吧

static class ThreadA extends Thread {@Overridepublic void run() {// TODO Auto-generated method stubsuper.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 stubthis.a = a;}@Overridepublic void run() {// TODO Auto-generated method stubsuper.run();System.out.println("ThreadB start");try {a.join();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.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();}

执行结果：

ThreadB startThreadA0ThreadA1ThreadA2ThreadA3ThreadA4ThreadA5ThreadA6ThreadA7ThreadA8ThreadA9ThreadB end

首先b线程执行，a线程join后，直接执行完a，然后才执行b，证实上述说法。

2、A.yield，A让出位置，给B执行，B执行结束A再执行。跟join意思正好相反！

static class ThreadA extends Thread {@Overridepublic void run() {// TODO Auto-generated method stubsuper.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 stubthis.a = a;}@Overridepublic void run() {// TODO Auto-generated method stubsuper.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 blocke.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();}

执行结果：

ThreadB startThreadA 0ThreadB 0ThreadA 1ThreadB 1ThreadA 2ThreadB 2ThreadB 3ThreadB 4ThreadB 5ThreadB 6ThreadB 7ThreadB 8ThreadB 9ThreadB endThreadA 3ThreadA 4ThreadA 5ThreadA 6ThreadA 7ThreadA 8ThreadA 9

首先B执行，然后A执行；在B的循环中，i=2时，A执行yield；接着B执行完，才轮到A执行。

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