join（）

代码：

package concurrent._join;

public class Demo {
    public static void main(String[] args) throws InterruptedException {
        ThreadA threadA = new ThreadA();
        ThreadB threadB = new ThreadB(threadA);

        String threadName = Thread.currentThread().getName();
        System.out.println(threadName + "已经启动了");
        threadB.run();

//        threadA.join();
//        System.out.println(threadName + "等待子线程的join方法结束了");


        threadB.join();
        System.out.println(threadName + "等待子线程的join方法结束了");

    }
}

class ThreadA extends  Thread{
    public ThreadA(){
        super("ThreadA");
    }
    @Override
    public void run() {
        String threadName = this.getName();
        System.out.println(threadName + "已经启动了");
        for(int i = 0 ; i < 5 ; i++){
            System.out.println(threadName + "开始第" + i + "次的睡眠");
            try {

                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(threadName + "已经结束了");

    }
}


class ThreadB extends  Thread{
    Thread thread;
    public ThreadB(Thread thread){
        super("ThreadB");
        this.thread = thread;
    }
    @Override
    public void run() {
        String threadName = this.getName();
        System.out.println(threadName + "已经启动了");
        try {
            thread.start();
            thread.join();
            System.out.println(threadName + "等待子线程的join方法结束了");

        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(threadName + "已经结束了");

    }
}

结果：

main已经启动了
ThreadB已经启动了
ThreadA已经启动了
ThreadA开始第0次的睡眠
ThreadA开始第1次的睡眠
ThreadA开始第2次的睡眠
ThreadA开始第3次的睡眠
ThreadA开始第4次的睡眠
ThreadA已经结束了
ThreadB等待子线程的join方法结束了
ThreadB已经结束了
main等待子线程的join方法结束了

修改代码：

package concurrent._join;

public class Demo {
    public static void main(String[] args) throws InterruptedException {
        ThreadA threadA = new ThreadA();
        ThreadB threadB = new ThreadB(threadA);

        String threadName = Thread.currentThread().getName();
        System.out.println(threadName + "已经启动了");
        threadA.start();
        threadB.start();
//        threadA.join();
//        System.out.println(threadName + "等待子线程的join方法结束了");


        threadB.join();
        System.out.println(threadName + "等待子线程的join方法结束了");

    }
}

class ThreadA extends  Thread{
    public ThreadA(){
        super("ThreadA");
    }
    @Override
    public void run() {
        String threadName = this.getName();
        System.out.println(threadName + "已经启动了");
        for(int i = 0 ; i < 5 ; i++){
            System.out.println(threadName + "开始第" + i + "次的睡眠");
            try {

                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(threadName + "已经结束了");

    }
}


class ThreadB extends  Thread{
    Thread thread;
    public ThreadB(Thread thread){
        super("ThreadB");
        this.thread = thread;
    }
    @Override
    public void run() {
        String threadName = this.getName();
        System.out.println(threadName + "已经启动了");
        try {
//            thread.start();
            thread.join();
            System.out.println(threadName + "等待子线程的join方法结束了");

        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(threadName + "已经结束了");

    }
}

结果：

main已经启动了
ThreadA已经启动了
ThreadA开始第0次的睡眠
ThreadB已经启动了
ThreadA开始第1次的睡眠
ThreadA开始第2次的睡眠
ThreadA开始第3次的睡眠
ThreadA开始第4次的睡眠
ThreadA已经结束了
ThreadB等待子线程的join方法结束了
ThreadB已经结束了
main等待子线程的join方法结束了