转自：https://blog.csdn.net/zzti_erlie/article/details/84926355
介绍
先看如下代码：
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| public class Test {
static Thread thread1 = new Thread(()-> {
System.out.println("thread1");
});
static Thread thread2 = new Thread(()-> {
System.out.println("thread2");
});
static Thread thread3 = new Thread(()-> {
System.out.println("thread3");
});
public static void main(String[] args) throws InterruptedException {
thread1.start();
thread2.start();
thread3.start();
}
}
|
重复执行多次，发现输出并不是按照线程的启动顺序来执行。因为这个里面涉及到CPU对线程的调度问题。
如何让 thread1，thread2，thread3 顺序执行呢？
方法1
通过join方法去保证多线程顺序执行
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| public class Test {
static Thread thread1 = new Thread(()-> {
System.out.println("thread1");
});
static Thread thread2 = new Thread(()-> {
System.out.println("thread2");
});
static Thread thread3 = new Thread(()-> {
System.out.println("thread3");
});
public static void main(String[] args) throws InterruptedException {
thread1.start();
thread1.join();
thread2.start();
thread2.join();
thread3.start();
}
}
|
可以看到输出一直是如下
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| thread1
thread2
thread3
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join 是怎么实现这个功能的呢？
join 方法让主线程等待子线程结束以后才能继续运行，因此保证了线程的顺序执行
方法2
使用单例线程池，用唯一的工作线程执行任务，保证所有任务按照指定顺序执行
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| ExecutorService executorService = Executors.newSingleThreadExecutor();
|
这个会把线程放在一个 FIFO 队列，依次执行线程
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| public class Test {
static Thread thread1 = new Thread(()-> {
System.out.println("thread1");
});
static Thread thread2 = new Thread(()-> {
System.out.println("thread2");
});
static Thread thread3 = new Thread(()-> {
System.out.println("thread3");
});
static ExecutorService executorService = Executors.newSingleThreadExecutor();
public static void main(String[] args) throws InterruptedException {
executorService.submit(thread1);
executorService.submit(thread2);
executorService.submit(thread3);
executorService.shutdown();
}
}
|
输出一直为