java-如何保证线程T1，T2，T3 按照顺序执行

调用join()方法

public class JoinTest {
    // 1.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
    public static void main(String[] args) {
         Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() { System.out.println("t1"); }
        });
         Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                //引用t1线程，等待t1线程执行完
                    t1.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("t2");
            }
        });
        Thread t3 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
            //引用t2线程，等待t2线程执行完
                    t2.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("t3");
            }
        });
        t3.start();
        t2.start();
        t1.start();
    }
}