如何保证多个线程按一定顺序执行

假设现在有三个线程t1、t2和t3
让t2在t1完成后执行,t3在t2完成后执行

自定义Thread类

public class Thread extends java.lang.Thread {
    private String str ;
    private int time;
    public Thread(String str,int time){
        this.str = str;
        this.time = time;
    }
    @Override
    public void run() {
        try {
            sleep(time);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(str);
    }
}

Main方法

public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread("t1",2000);
        Thread t2 = new Thread("t2",1000);
        Thread t3 = new Thread("t3",500);
        t1.start();
        t1.join();
        t2.start();
        t2.join();
        t3.start();
        t3.join();
        System.out.println("main");
    }

执行结果

join方法参考文章：【Java】Thread类中的join()方法原理