线程--join()方法的介绍

一、join()方法，官方描述 waits for this thread to die 等待当前线程死亡；

源码：

//无参，默认调用join(0)

public final void join() throws InterruptedException {

join(0);

}

//传入两时间millis 毫秒+nanos纳秒，表示等等millis+nanos,最终还是调用了方法3

public final synchronized void join(long millis, int nanos)

throws InterruptedException {

if (millis < 0) {

throw new IllegalArgumentException("timeout value is negative");

}

if (nanos < 0 || nanos > 999999) {

throw new IllegalArgumentException(

"nanosecond timeout value out of range");

}

if (nanos >= 500000 || (nanos != 0 && millis == 0)) {

millis++;

}

join(millis);

}

//方法3：传入等时间，单位为毫秒，底层调用Object的wait(time)

public final synchronized void join(long millis)

throws InterruptedException {

long base = System.currentTimeMillis();

long now = 0;

if (millis < 0) {

throw new IllegalArgumentException("timeout value is negative");

}

if (millis == 0) {

while (isAlive()) {

wait(0);//表示一直等待，指导线程死亡

}

} else {

while (isAlive()) {

long delay = millis - now;

if (delay <= 0) {

break;

}

wait(delay);

now = System.currentTimeMillis() - base;

}

}

}

二、应用，比如几个线程要按一定顺序执行

public class ThreadJoin extends Thread {

public void run(){

try {

this.sleep(500);

System.out.println("["+new Date()+"]"+this.getName());

} catch (InterruptedException e) {

e.printStackTrace();

}

}

public static void main(String[] args) throws Exception {

int length = 5;

Thread[] threads = new Thread[length];

for(int i=0; i<length;i++){

threads[i] = new ThreadJoin();

threads[i].start();

threads[i].join();//每个线程开启后都调用join

}

long endTime=System.currentTimeMillis();

}

}

/*

output:

[Sun Jun 11 13:40:42 CST 2017]Thread-0

[Sun Jun 11 13:40:43 CST 2017]Thread-1

[Sun Jun 11 13:40:43 CST 2017]Thread-2

[Sun Jun 11 13:40:44 CST 2017]Thread-3

[Sun Jun 11 13:40:44 CST 2017]Thread-4

如果把join()注释

结果可能每次都不一样

[Sun Jun 11 13:51:09 CST 2017]Thread-2

[Sun Jun 11 13:51:09 CST 2017]Thread-4

[Sun Jun 11 13:51:09 CST 2017]Thread-1

[Sun Jun 11 13:51:09 CST 2017]Thread-3

[Sun Jun 11 13:51:09 CST 2017]Thread-0

*/

做事不能急，给自己一个大方向后总得一步一步来

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