一、计时器

Java的标准库中,为我们提供了 计时器 的实现,让我们先来试着使用它.

 public static void main(String[] args) throws InterruptedException{Timer timer = new Timer();timer.schedule(new TimerTask() {@Overridepublic void run() {System.out.println("hello timer 3000");}},3000);timer.schedule(new TimerTask() {@Overridepublic void run() {System.out.println("hello timer 2000");}},2000);timer.schedule(new TimerTask() {@Overridepublic void run() {System.out.println("hello timer 1000");}},1000);System.out.println("hello main");Thread.sleep(5000);timer.cancel();}

创建timer实例后,我们可以调用schedule方法进行传参,第一个参数是要执行的方法,第二个参数是需要等待的时间.

二、实现计时器

让我们尝试来实现一个简单的计时器

当a创建好后,使用schedule,就会创建出一个线程,来查看是否有需要执行的任务.

传入的run方法会构造出一个Runnable放入队列中等待执行.

没有就等待,有就把任务从队列中删除并执行.

class MyTimerTask2 implements Comparable<MyTimerTask2>{private Runnable runnable;private long time;public MyTimerTask2(Runnable runnable,long delay){this.runnable = runnable;this.time = System.currentTimeMillis()+delay;}public void run(){runnable.run();}public long getTime(){return time;}@Overridepublic int compareTo(MyTimerTask2 o) {return (int)(this.time-o.time);}
}class MyTimer2{Thread t = null;private PriorityQueue<MyTimerTask2> queue= new PriorityQueue<>();private Object locker = new Object();public void schedule(Runnable runnable,long delay){synchronized (locker){MyTimerTask2 task = new MyTimerTask2(runnable,delay);queue.offer(task);locker.notify();}}public void cancel(){t.interrupt();}public MyTimer2(){//查看队列是否可以执行t = new Thread(()->{while(!Thread.currentThread().isInterrupted()){try{synchronized (locker){while(queue.isEmpty()){locker.wait();}MyTimerTask2 task = queue.peek();long nowtime = System.currentTimeMillis();if(nowtime>=task.getTime()){queue.poll();task.run();}else {locker.wait(task.getTime() - nowtime);}}} catch(InterruptedException e){break;}}System.out.println("线程执行完成");});t.start();}
}public class ThreadDemo05 {public static void main(String[] args) throws InterruptedException{MyTimer2 a = new MyTimer2();a.schedule(new Runnable() {@Overridepublic void run() {System.out.println("hello ");}},3000);System.out.println("hello main");//Thread.sleep(3500);a.cancel();}
}