控制线程的执行顺序

通过join方法保证多线程的顺序性特性

   static Thread thread1 = new Thread(new Runnable() {
        @Override
        public void run() {
            System.out.println("thread1");
        }
    });
    static Thread thread2 = new Thread(new Runnable() {
        @Override
        public void run() {
            System.out.println("thread2");
        }
    });
    static Thread thread3 = new Thread(new Runnable() {
        @Override
        public void run() {
            System.out.println("thread3");
        }
    });
    public static void main(String[] args) throws InterruptedException {
        thread1.start();
        thread1.join();
        thread2.start();
        thread2.join();
        thread3.start();
        thread3.join();
    }

join

让主线程等待子线程结束以后才能继续运行，执行流程如下：

执行流程.jpg

通过线程池保证多线程的顺序性特性

  static Thread thread1 = new Thread(new Runnable() {
        @Override
        public void run() {
            System.out.println("thread1");
        }
    });
    static Thread thread2 = new Thread(new Runnable() {
        @Override
        public void run() {
            System.out.println("thread2");
        }
    });
    static Thread thread3 = new Thread(new Runnable() {
        @Override
        public void run() {
            System.out.println("thread3");
        }
    });
    
    static ExecutorService executorService = Executors.newSingleThreadExecutor();

    public static void main(String[] args) throws InterruptedException {
        executorService.execute(thread1);
        executorService.execute(thread2);
        executorService.execute(thread3);

        executorService.shutdown();
    }

源码

创建只有一个线程的线程池，适用于需要保证顺序地执行各个任务；并且在任意时间点，不会有多个线程是活动的应用场景。

public static ExecutorService newSingleThreadExecutor() {
        return new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>()));
    }