join用法

join的作用

join可以让线程排队执行，而join的内部采用wait方法来实现等待。而join的作用是等待线程对象销毁。

public class MyThread extends Thread {

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + " run start");
        
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        System.out.println(Thread.currentThread().getName() + "run end");
    }
}

public class JoinTest {

    public static void main(String[] args) {
        MyThread mt = new MyThread();
        mt.setName("MyThread");
        mt.start();
        
        try {
            mt.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        System.out.println(Thread.currentThread().getName() + " execute");
    }
}

join(long time)设置等待时间

public class JoinTest {

    public static void main(String[] args) {
        Thread t1 = new Thread(new Runnable() {

            @Override
            public void run() {
                System.out.printf("%s start %d\n", Thread.currentThread().getName(), System.currentTimeMillis());
                
                try {
                    Thread.sleep(6000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                
                System.out.printf("%s end %d\n", Thread.currentThread().getName(), System.currentTimeMillis());
            }
        });
        
        t1.setName("t1");
        t1.start();
        
        try {
            t1.join(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        System.out.printf("%s start %d\n", Thread.currentThread().getName(), System.currentTimeMillis());
    }
}

结果：

t1 start 1541408642457
main start 1541408644457
t1 end 1541408648500

说明：可以发现在join设置的时间到时之后，将会让join的线程等待，让其他的线程执行。也可以看到join到时间将释放锁。