T1，T2，T3 三个线程顺序执行

T1，T2，T3 三个线程顺序执行

现在有 T1、T2、T3 三个线程，你怎样保证 T2 在 T1 执行完后执行，T3 在 T2 执行完后执行？(T1->T2->T3)

这个线程问题通常会在第一轮或电话面试阶段被问到，目的是检测你对"join"方法是否熟悉。

public class TestThreadJoin {
    public static void main(String[] args) {
        method01();
        method02();
    }

    // 第一种实现方式，顺序写死在线程代码的内部了，有时候不方便。
    private static void method01() {
        final Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("t1 is finished");
            }
        });

        final Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    t1.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("t2 is finished");
            }
        });

        Thread t3 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    t2.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("t3 is finished");
            }
        });
        t3.start();
        t2.start();
        t1.start();
    }

    // 第二种实现方式，线程执行顺序可以在方法中调换。
    private static void method02() {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread().getName() + "执行完成");
            }
        };
        Thread t1 = new Thread(runnable, "t1");
        Thread t2 = new Thread(runnable, "t2");
        Thread t3 = new Thread(runnable, "t3");
        t1.start();
        try {
            t1.join();
            t2.start();
            t2.join();
            t3.start();
            t3.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

点击查看结果

```
t1 is finished
t1执行完成
t2 is finished
t3 is finished
t2执行完成
t3执行完成

Process finished with exit code 0

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