Ali: How many methods are there for multi-threaded sequential operation?

文章介绍4种方法,简单易懂,通过4个demo抛砖引玉.

1、在子线程中通过join()方法指定顺序

通过join()方法使当前线程“阻塞”,

“”

运行结果：

2、在主线程中通过join()方法指定顺序

子线程指的是发生在Thread内部的代码,主线程指的是发生在main函数中的代码.最新多线程面试题整理好了,点击Java面试库小程序在线刷题.

我们可以在main函数中通过join()方法让主线程阻塞等待以达到指定顺序执行的目的.

public class ThreadMainJoinDemo {
    public static void main(String[] args) throws InterruptedException {
        final Thread thread1 = new Thread(new  Runnable() {
            @Override
            public void  run() {
                System.out.println( "打开冰箱！");
            }
        });
 
        final Thread thread2 = new Thread(new  Runnable() {
            @Override
            public void  run() {
                System.out.println( "拿出一瓶牛奶！");
            }
        });
 
        final Thread thread3 = new Thread(new  Runnable() {
            @Override
            public void  run() {
                System.out.println( "关上冰箱！");
            }
        });
 
        thread1.start();
        thread1.join();
        thread2.start();
        thread2.join();
        thread3.start();
    }
}

基础就不介绍了,多线程系列我博客教程写了很多了,这里推荐大家看看吧：https://www.javastack.cn/categories/Java/

输出结果：

打开冰箱！
拿出一瓶牛奶！
关上冰箱！

3、通过倒数计时器CountDownLatch实现

CountDownLatch通过计数器提供了更灵活的控制,只要检测到计数器为0当前线程就可以往下执行而不用管相应的thread是否执行完毕.

public class ThreadCountDownLatchDemo {
 
    private static CountDownLatch countDownLatch1 = new CountDownLatch(1);
 
    private static CountDownLatch countDownLatch2 = new CountDownLatch(1);
 
    public static void main(String[] args) {
        final Thread thread1 = new Thread(new  Runnable() {
            @Override
            public void  run() {
                System.out.println( "打开冰箱！");
                countDownLatch1.countDown();
            }
        });
 
        final Thread thread2 = new Thread(new  Runnable() {
            @Override
            public void  run() {
                try {
                    countDownLatch1.await();
                    System.out.println( "拿出一瓶牛奶！");
                    countDownLatch2.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
 
        final Thread thread3 = new Thread(new  Runnable() {
            @Override
            public void  run() {
                try {
                    countDownLatch2.await();
                    System.out.println( "关上冰箱！");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
 
        //下面三行代码顺序可随意调整,程序运行结果不受影响
        thread3.start();
        thread1.start();
        thread2.start();
    }
}
打开冰箱！
拿出一瓶牛奶！
关上冰箱！

单线程化线程池(newSingleThreadExecutor)的优点,串行执行所有任务.

输出结果：

打开冰箱！
拿出一瓶牛奶！
关上冰箱！