java 多线程 Thread.join子线程结束父线程再运行；join(long)：等待超时毫秒数

Join的使用

目的：当子线程运行结束后，父线程才能再继续运行

/**
 * @ClassName ThreadJoinExample
 * @projectName: object1
 * @author: Zhangmingda
 * @description： XXX
 * date: 2021/4/24.
 */
public class ThreadJoinExample {
    public static void main(String[] args) throws InterruptedException {
        Runnable r = new Runnable() {
            @Override
            public void run() {
                String tName = Thread.currentThread().getName();
                try {
                    System.out.println(tName + "开始运行");
                    Thread.sleep(4000);
                    System.out.println(tName +"运行结束！");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        Thread thread = new Thread(r,"子任务1");
        Thread thread2 = new Thread(r,"子任务2");
        thread.start();
        thread2.start();
        thread.join(); //子线程阻塞主线程，待子线程运行结束
        thread2.join(); //子线程阻塞主线程，待子线程运行结束
        Thread.sleep(1000);
        System.out.println("主线程运行结束！");
    }
}

 不能interrupt中断一个有join()子线程的父线程

/**
 * @ClassName ThreadInterruptJoinThread
 * @projectName: object1
 * @author: Zhangmingda
 * @description： XXX
 * date: 2021/4/24.
 */
public class ThreadInterruptJoinThread {
    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread("parent"){
            @Override
            public void run() {
                System.out.println(getName() + "开始运行");
                Thread thread1 = new Thread("child"){
                    @Override
                    public void run() {
                        System.out.println(getName() + "开始运行");
                        try {
                            Thread.sleep(3000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        System.out.println(getName() + "运行结束");
                    }
                };
                thread1.start();
                //thread1.join();
                try {
                    thread1.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(getName() + "运行结束");
            }
        };
        thread.start();
        Thread.sleep(1000);
        thread.interrupt();
        thread.join();
        System.out.println("主线程运行结束");
    }
}

如上代码执行结果：join的child子线程还没结束，父线程就被interrupt中断，会导致父线程异常，且不再等待子线程child运行结束。

join(long)：等待指定时间不结束就不等待了

/**
 * @ClassName ThreadJoinTime
 * @projectName: object1
 * @author: Zhangmingda
 * @description： XXX
 * date: 2021/4/24.
 */
public class ThreadJoinTime {
    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread("child"){
            @Override
            public void run() {
                System.out.println("子线程开始运行");
                try {
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("子线程运行结束");
            }
        };
        thread.start();
        thread.join(1000);
        System.out.println("主线程代码运行结束");
    }
}