//簡(jiǎn)單定時(shí)器
public class TestTimer {
    //每個(gè) Task 實(shí)例 就包含一個(gè)要執(zhí)行的任務(wù)
    //Task 要放到一個(gè)優(yōu)先級(jí)隊(duì)列中，但是優(yōu)先級(jí)隊(duì)列里面是需要比較優(yōu)先級(jí)的
    static class Task implements Comparable<Task>{
        //什么時(shí)候執(zhí)行
        private long time;
        //執(zhí)行什么任務(wù)
        private  Runnable command;

        public Task(Runnable command ,long time){
            this.command = command;
            this.time = System.currentTimeMillis()+time;
        }

        public void  run(){
        //執(zhí)行Runable 里面的run方法
            command.run();
        }

        @Override
        public int compareTo(Task o) {
            return (int)(this.time - o.time);
        }
    }
    static class Timer{
        //先創(chuàng)建一個(gè)帶優(yōu)先級(jí)的阻塞隊(duì)列
        private PriorityBlockingQueue<Task>  queue = new PriorityBlockingQueue<>();

        //用這個(gè)對(duì)象來(lái)完成線程之間的協(xié)調(diào)任務(wù)
        private Object meilbox = new Object();

        //schedule 方法就是把一個(gè)Task 放在Timer中
        public void schedule(Runnable command,long after){
            Task task = new Task(command,after);
            //將當(dāng)前任務(wù)放入對(duì)列
            queue.put(task);
            //當(dāng)worker 線程中包含wait機(jī)制的時(shí)候，在安排任務(wù)的時(shí)候就需要顯示的喚醒一下
            synchronized (meilbox){
                meilbox.notify();
            }
        }
        //寫一個(gè)構(gòu)造方法，創(chuàng)建線程
        public Timer(){
            //創(chuàng)建一個(gè)線程，讓這個(gè)線程去掃描隊(duì)列的隊(duì)首元素，看看能不能執(zhí)行
            Thread worker = new Thread(){
                @Override
                public void run() {
                    //取出隊(duì)首元素，判斷這個(gè)元素能不能執(zhí)行
                    while(true){
                        try {
                            Task task = queue.take();
                            long currTime = System.currentTimeMillis();
                            if(currTime >= task.time){
                                //時(shí)間到，執(zhí)行任務(wù)
                                task.run();
                            }else{
                                //時(shí)間沒(méi)到，繼續(xù)等待
                                queue.put(task);
                                synchronized (meilbox){
                                    meilbox.wait(task.time-currTime);
                                }
                            }
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            };
            worker.start();
        }
    }
}

public static void main(String[] args) {
        Timer timer = new Timer();
        Runnable command = new Runnable() {
            @Override
            public void run() {
                System.out.println("時(shí)間到了~");
               // timer.schedule(this,3000); 每隔3是就執(zhí)行一次
            }
        };
        System.out.println("安排任務(wù)");
        timer.schedule(command,3000);
    }
}