实现一个定时器

1.Java自带的定时器

public class Test9 {

    public static void main(String[] args) {
        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("1000");
            }
        },1000);
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("3000");
            }
        },3000);
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("2000");
            }
        },2000);
        System.out.println("启动");
    }

}

2.自己实现一个定时器

//用来描述任务的一个类
class MyTimerTask implements Comparable<MyTimerTask>{
    private long time;//执行任务的时间
    private Runnable runnable;//要执行的任务

    public MyTimerTask(Runnable runnable,long delay) {
        this.runnable = runnable;
        this.time = System.currentTimeMillis()+delay;
    }

    public long getTime() {
        return this.time;
    }

    public Runnable getRunnable() {
        return runnable;
    }

    @Override
    public int compareTo(MyTimerTask o) {//优先级队列要设定一个比较队列中元素的规则
        return (int) (this.time-o.time);//这个写法是最小的元素位于队首
    }
}

//自己要实现的计时器
class MyTimer{
    PriorityQueue<MyTimerTask> queue = new PriorityQueue<>();//利用优先级队列存储任务
    Object lock = new Object();//定义一把锁
    public void schedule(Runnable runnable,long delay) {//执行任务的方法
        synchronized (lock) {
            queue.offer(new MyTimerTask(runnable,delay));
            lock.notify();//这里可以唤醒队列为空的情况和有新的任务加入到队列当中
        }
    }

    //再写一个扫描线程，去判断任务需不需要执行
    public MyTimer() {

        Thread t = new Thread(()->{
            while (true) {
                try {
                    synchronized (lock) {
                        while (queue.isEmpty()) {//如果队列为空则wait等待，所以要搭配synchronized
                            lock.wait();
                        }
                        long curTime = System.currentTimeMillis();
                        MyTimerTask task = queue.peek();
                        if (curTime >= task.getTime()) {//将当前的时间与队首任务的时间做对比
                            task.getRunnable().run();//执行任务
                            queue.poll();//执行完任务，从队列里面删除
                        }else {
                            lock.wait(task.getTime()-curTime);//当任务时间没到的时候，让其等待，
                        }
                    }
                }catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        t.start();
    }

}
public class Test9 {

    public static void main(String[] args) {
        MyTimer myTimer = new MyTimer();
        myTimer.schedule(new Runnable() {
            @Override
            public void run() {
                System.out.println("1000");
            }
        }, 1000);
        myTimer.schedule(new Runnable() {
            @Override
            public void run() {
                System.out.println("3000");
            }
        },3000);
        myTimer.schedule(new Runnable() {
            @Override
            public void run() {
                System.out.println("2000");
            }
        },2000);
    }

}