起三个线程，按指定顺序执行，在需要后执行的线程执行过程中，让前一个线程先执行，即Thread_after中调用Thread_before.jion()

public class ThreadLoop {


    static Thread t1 = new Thread(new Runnable() {
        @SneakyThrows
        @Override
        public void run() {
            System.out.println("t1");
        }
    });


    static Thread t2 = new Thread(new Runnable() {
        @Override
        @SneakyThrows
        public void run() {
            t1.join();// 等t1运行完，继续t2
            System.out.println("t2");
        }
    });


    static Thread t3 = new Thread(new Runnable() {
        @Override
        @SneakyThrows
        public void run() {
            t2.join();// 等t2运行完，继续t3
            System.out.println("t3");
        }
    });


    public static void main(String[] args) {

        t2.start();
        t1.start();
        t3.start();
    }
}