线程中的join

现创建两个线程thread1和thread2，thread1运行时间短，thread2运行时间长，代码如下：

    public static void main(String[] args) throws InterruptedException {
        Thread thread1 = new Thread(() -> {//运行时间短
            for (int i = 0; i < 3; i++) {
                System.out.println("Thread1");
                try {
                    sleep(1000);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
        });
        Thread thread2 = new Thread(() -> {//运行时间长
            for (int i = 0; i < 3; i++) {
                System.out.println("Thread2");
                try {
                    sleep(2000);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
        });
        thread1.start();
        thread2.start();

        for (int i = 0; i < 3; i++) {
            System.out.println("main");
            sleep(1000);
        }
    }

现有如下join顺序：

1.

thread1.join();

会使main线程阻塞，thread1与thread2同时运行，由于thread1运行时间短，则thread1会先结束，结束后thread2与main同时运行。

2.

thread2.join();

会使mian线程阻塞，thread1与thread2同时运行，thread1结束后，thread2依然在运行，thread2结束后main才会运行。

3.

thread1.join();

thread2.join();

mian线程被阻塞，thread1与thread2先运行，thread1结束后thread2依然在运行，thread2结束后mian才运行。

4. 

thread2.join();

thread1.join();

main线程被阻塞，thread1与thread2先运行，由于thread1先于thread2结束，则thread2结束后“thread1.join()”是无效语句，mian接着运行。

以上3，4的写法与2是等价的