Java让多线程按顺序执行的几种方法

目录在子线程中通过join(DOdpF)方法指定顺序在主线程中通过join()方法指定顺序通过倒数计时器CountDownLatch实现通过创建单一化线程池newSingleThreadExecutor()实现

文章介绍4种方法，简单易懂，通过4个demo抛砖引玉。

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”，等待指定线程执行完毕后继续执行。举例：在线程thread2中，加上一句thread1.join()，其意义在于，当前线程2运行到此行代码时会进入阻塞状态，直到线程thread1执行完毕后，线程thread2才会继续运行，这就保证了线程thread1与线程thread2的运行顺序。

public class ThreadJoinDemo {

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() {

try {

thread1.join();

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println("拿出一瓶牛奶！");

}

});

final Thread thread3 = new Thread(new Runnable() {

@Override

public void run() {

try {

thread2.join();

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println("关上冰箱！");

}

});

//下面三行代码顺序可随意调整，程序运行结果不受影响，因为我们在子线程中通过“join()方法”已经指定了运行顺序。

thread3.start();

thread2.start();

thread1.start();

}

}

运行结果：

打开冰箱！拿出一瓶牛奶！关上冰箱！

在主线程中通过join()方法指定顺序

简单说一下子线程与主线程的区别，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，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();

}

}

输出结果：

打开冰箱！拿出一瓶牛奶！关上冰箱！

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(DOdpF1);

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();

}

}

输出结果：

打开冰箱！拿出一瓶牛奶！关上冰箱！

通过创建单一化线程池newSingleThreadExecutor()实现

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

public class ThreadPoolDemo {

static ExecutorService executorService = Executors.newSingleThreadExecutor();

public static void main(String[] args) {

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

pDOdpFublic 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！");

}

});

executorService.submit(thread1);

executorService.submit(thread2);

executorService.submit(thread3);

executorService.shutdown(); //使用完毕记得关闭线程池

}

}

输出结果：

打开冰箱！拿出一瓶牛奶！关上冰箱！

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