定义

等待该线程终止，比如 A 线程调用了 B 线程的 join，那么 A 线程要等到 B 线程执行完后，才可以继续执行。

示例

public class JoinDemo {
    static class JoinThread1 implements Runnable {
        Thread thread;

        public JoinThread1(Thread thread) {this.thread = thread;}

        @Override
        public void run() {System.out.println("thread1 start");
            try {thread.join();
                System.out.println("thread1 end");
            } catch (InterruptedException e) {e.printStackTrace();
            }
        }
    }

    static class JoinThread2 implements Runnable {
        @Override
        public void run() {System.out.println("thread2 start");
            try {Thread.sleep(10000);
                System.out.println("thread2 end");
            } catch (InterruptedException e) {e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {JoinThread2 joinThread2 = new JoinThread2();
        Thread thread2 = new Thread(joinThread2);
        JoinThread1 joinThread1 = new JoinThread1(thread2);
        Thread thread1 = new Thread(joinThread1);

        thread1.start();
        thread2.start();}
}

运行结果如下：

线程 1 执行的时候，调用线程 2 的 join，线程 1 不休眠，线程 2 休眠了 10 秒，从结果看出来，线程 2 执行完后，线程 1 才执行完。