import java.util.Timer;
import java.util.TimerTask;

public class Demo {
    public static void main(String[] args) {
        //Timer內(nèi)部是專門有線程來執(zhí)行我們注冊的任務(wù),這個線程在執(zhí)行完一個任務(wù)還會等待別的任務(wù)執(zhí)行
        Timer timer = new Timer();
        //schedule(任務(wù)，多久后執(zhí)行任務(wù))
        //TimerTask是一個抽象類，實現(xiàn)了Runnable接口
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("hello timer");
            }
        }, 3000);

        System.out.println("main");
    }
}

//描述任務(wù)
class MyTask implements Comparable<MyTask>{
    //任務(wù)具體的內(nèi)容
    private Runnable runnable;
    //任務(wù)執(zhí)行的時間戳
    private long time;

    //delay為時間間隔，不是具體的時間戳
    public MyTask(Runnable runnable, long delay){
        this.runnable = runnable;
        this.time = System.currentTimeMillis()+delay;
    }

    @Override
    public int compareTo(MyTask o) {
        return (int) (this.time-o.time);
    }

    public void run(){
        runnable.run();
    }


    public long getTime() {
        return time;
    }

}

    private PriorityBlockingQueue<MyTask> p = new PriorityBlockingQueue<>();
    //創(chuàng)建一個對象用于加鎖
    private Object locker = new Object();
    public void schedule(Runnable runnable, long delay){
        MyTask task = new MyTask(runnable, delay);
        p.put(task);
        //插入任務(wù)，可能執(zhí)行時間已經(jīng)過了，需要喚醒等待的線程進行判斷是否執(zhí)行
        synchronized (locker){
            locker.notify();
        }
    }

       public MyTimer(){
        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                while(true){
                    try {
                        MyTask task = p.take();
                        if(task.getTime() > System.currentTimeMillis()){
                            p.put(task);
                            //當(dāng)執(zhí)行時間沒到時，沒必要一直進行判斷，比較耗費CPU
                            //所以等待一定時間
                            synchronized (locker){
                                locker.wait(task.getTime()-System.currentTimeMillis());
                            }
                        }else {
                            task.run();
                        }
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        });
        t.start();
    }