public abstract class TimerTask implements Runnable // jdk源碼

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

public class TestProgram {
    public static void main(String[] args) {
        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("執(zhí)行延后3s的任務(wù)!");
            }
        }, 3000);

        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("執(zhí)行延后2s后的任務(wù)!");
            }
        }, 2000);
        
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("執(zhí)行延后1s的任務(wù)!");
            }
        }, 1000);
    }
}

class MyTask implements Comparable<MyTask>{
    //要執(zhí)行的任務(wù)
    private Runnable runnable;
    //任務(wù)的執(zhí)行時間
    private long time;

    public MyTask(Runnable runnable, long time) {
        this.runnable = runnable;
        this.time = time;
    }

    //獲取當(dāng)前任務(wù)的執(zhí)行時間
    public long getTime() {
        return this.time;
    }
    //執(zhí)行任務(wù)
    public void run() {
        runnable.run();
    }

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

private PriorityBlockingQueue<MyTask> queue = new PriorityBlockingQueue<>();

//自己實現(xiàn)的定時器類
class MyTimer {
    //掃描線程
    private Thread t = null;
    //阻塞隊列,存放任務(wù)
    private PriorityBlockingQueue<MyTask> queue = new PriorityBlockingQueue<>();

    public MyTimer() {
        //構(gòu)造掃描線程
        t = new Thread(() -> {
           while (true) {
               //取出隊首元素,檢查隊首元素執(zhí)行任務(wù)的時間
               //時間沒到,再把任務(wù)放回去
               //時間到了,就執(zhí)行任務(wù)
               try {
                   synchronized (this) {
                       MyTask task = queue.take();
                       long curTime = System.currentTimeMillis();
                       if (curTime < task.getTime()) {
                           //時間沒到,放回去
                           queue.put(task);
                           //放回任務(wù)后,不應(yīng)該立即就再次取出該任務(wù)
                           //所以wait設(shè)置一個阻塞等待,以便新任務(wù)到時間或者新任務(wù)來時后再取出來
                           this.wait(task.getTime() - curTime);
                       } else {
                           //時間到了,執(zhí)行任務(wù)
                           task.run();
                       }
                   }
               } catch (InterruptedException e) {
                   throw new RuntimeException(e);

               }
           }
        });
        t.start();
    }

    /**
     * 注冊任務(wù)的方法
     * @param runnable 任務(wù)內(nèi)容
     * @param after 表示在多少毫秒之后執(zhí)行. 形如 1000
     */
    public void schedule (Runnable runnable, long after) {
        //獲取當(dāng)前時間的時間戳再加上任務(wù)時間
        MyTask task = new MyTask(runnable, System.currentTimeMillis() + after);
        queue.put(task);
        //每次當(dāng)新任務(wù)加載到阻塞隊列時,需要中途喚醒線程,因為新進來的任務(wù)可能是最早需要執(zhí)行的
        synchronized (this) {
            this.notify();
        }
    }
}

public class TestDemo23 {
    public static void main(String[] args) {
        MyTimer timer = new MyTimer();
        timer.schedule(new Runnable() {
            @Override
            public void run() {
                System.out.println("2s后執(zhí)行的任務(wù)1");
            }
        }, 2000);

        timer.schedule(new Runnable() {
            @Override
            public void run() {
                System.out.println("2s后執(zhí)行的任務(wù)1");
            }
        }, 1000);
    }
}