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 {
@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();
}
执行结果：
ThreadB start ThreadA0 ThreadA1 ThreadA2 ThreadA3 ThreadA4 ThreadA5 ThreadA6 ThreadA7 ThreadA8 ThreadA9 ThreadB 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 {
@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();
}
执行结果：
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
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。