public class ThreadTest {    class MyTask implements Runnable{        public void run() {            say();        }    }    public void init(){        say();        MyTask myTask = new MyTask();        ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1);        executorService.scheduleAtFixedRate(myTask,5,5,TimeUnit.SECONDS);    }    public static void say(){        System.out.println("Hello world");    }    public static void main(String[] args)  {        ThreadTest threadTest = new ThreadTest();        threadTest.init();    }}

　　这个程序执行了之后，在运行这个程序后的5秒（scheduleAtFixedRate的第二个参数决定）之后，每5秒(scheduleAtFixedRate的第三个参数决定)执行一个say().