Timer timer = new Timer();
timer.schedule(new TimerTask() {
@Override
public void run() {
System.out.println("hello");
}
}, 3000);

public class Test {
    public static void main(String[] args){
        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("執(zhí)行線程在5s后執(zhí)行");
            }
        },5000);
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("執(zhí)行線程在2s后執(zhí)行");
            }
        },2000);
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("執(zhí)行線程在3s后執(zhí)行");
            }
        },3000);
    }
}

class MyTask implements Comparable<MyTask>{
    //執(zhí)行的時(shí)間戳
    private long time;
    //接受具體任務(wù)
    private Runnable runnable;
    //創(chuàng)建MyTask構(gòu)造方法
    public MyTask(Runnable runnable,long time) {
        //通過(guò)currentTimeMillis來(lái)獲取time 中存的是絕對(duì)時(shí)間, 超過(guò)這個(gè)時(shí)間的任務(wù)就應(yīng)該被執(zhí)行
        this.time = System.currentTimeMillis()+time;
        this.runnable = runnable;
    }
    //執(zhí)行任務(wù)
    public void run(){
        this.runnable.run();
    }
    //提供對(duì)外time
    public long getTime() {
        return time;
    }
    //執(zhí)行comparable接口來(lái)進(jìn)行時(shí)間的比較,并將time的long類型轉(zhuǎn)換為int類型
    @Override
    public int compareTo(MyTask o) {
        return (int)(this.time-o.time);
    }
}

class MyTimer{
    // 定時(shí)器內(nèi)部要能夠存放多個(gè)任務(wù)
    private PriorityBlockingQueue<MyTask> queue = new PriorityBlockingQueue<>();
    //為鎖創(chuàng)建一個(gè)對(duì)象
    Object locker = new Object();
    public void schedule(Runnable runnable, long delay) {
        MyTask task = new MyTask(runnable, delay);
        queue.put(task);
        // 每次任務(wù)插入成功之后, 都喚醒一下掃描線程, 讓線程重新檢查一下隊(duì)首的任務(wù)看是否時(shí)間到要執(zhí)行~~
        synchronized (locker) {
            locker.notify();
        }
    }

class MyTimer{
    // 定時(shí)器內(nèi)部要能夠存放多個(gè)任務(wù)
    private PriorityBlockingQueue<MyTask> queue = new PriorityBlockingQueue<>();
    //為鎖創(chuàng)建一個(gè)對(duì)象
    Object locker = new Object();
    public void schedule(Runnable runnable, long delay) {
        MyTask task = new MyTask(runnable, delay);
        queue.put(task);
        // 每次任務(wù)插入成功之后, 都喚醒一下掃描線程, 讓線程重新檢查一下隊(duì)首的任務(wù)看是否時(shí)間到要執(zhí)行~~
        synchronized (locker) {
            locker.notify();
        }
    }
    public MyTimer() {
        Thread t = new Thread(() -> {
            while (true) {
                try {
                    // 先取出隊(duì)首元素
                    MyTask task = queue.take();
                    // 再比較一下看看當(dāng)前這個(gè)任務(wù)時(shí)間到了沒(méi)?
                    long curTime = System.currentTimeMillis();
                    if (curTime < task.getTime()) {
                        // 時(shí)間沒(méi)到, 把任務(wù)再塞回到隊(duì)列中.
                        queue.put(task);
                        // 指定一個(gè)等待時(shí)間,防止有的線程需要等待時(shí)間很長(zhǎng)，但是線程一直運(yùn)行等待時(shí)間到來(lái)執(zhí)行，這樣會(huì)占有CPU占有資源
                        synchronized (locker) {
                            locker.wait(task.getTime() - curTime);
                        }
                    } else {
                        // 時(shí)間到了, 執(zhí)行這個(gè)任務(wù)
                        task.run();
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        t.start();
    }
}

package thread;

import java.util.PriorityQueue;
import java.util.concurrent.PriorityBlockingQueue;

// 創(chuàng)建一個(gè)類, 表示一個(gè)任務(wù).
class MyTask implements Comparable<MyTask> {
    // 任務(wù)具體要干啥
    private Runnable runnable;
    // 任務(wù)具體啥時(shí)候干. 保存任務(wù)要執(zhí)行的毫秒級(jí)時(shí)間戳
    private long time;

    // after 是一個(gè)時(shí)間間隔. 不是絕對(duì)的時(shí)間戳的值
    public MyTask(Runnable runnable, long delay) {
        this.runnable = runnable;
        this.time = System.currentTimeMillis() + delay;
    }

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

    public long getTime() {
        return time;
    }

    @Override
    public int compareTo(MyTask o) {
        // 到底是誰(shuí)見(jiàn)誰(shuí), 才是一個(gè)時(shí)間小的在前? 需要咱們背下來(lái).
        return (int) (this.time - o.time);
    }
}

class MyTimer {
    // 定時(shí)器內(nèi)部要能夠存放多個(gè)任務(wù)
    private PriorityBlockingQueue<MyTask> queue = new PriorityBlockingQueue<>();

    public void schedule(Runnable runnable, long delay) {
        MyTask task = new MyTask(runnable, delay);
        queue.put(task);
        // 每次任務(wù)插入成功之后, 都喚醒一下掃描線程, 讓線程重新檢查一下隊(duì)首的任務(wù)看是否時(shí)間到要執(zhí)行~~
        synchronized (locker) {
            locker.notify();
        }
    }

    private Object locker = new Object();

    public MyTimer() {
        Thread t = new Thread(() -> {
            while (true) {
                try {
                    // 先取出隊(duì)首元素
                    MyTask task = queue.take();
                    // 再比較一下看看當(dāng)前這個(gè)任務(wù)時(shí)間到了沒(méi)?
                    long curTime = System.currentTimeMillis();
                    if (curTime < task.getTime()) {
                        // 時(shí)間沒(méi)到, 把任務(wù)再塞回到隊(duì)列中.
                        queue.put(task);
                        // 指定一個(gè)等待時(shí)間
                        synchronized (locker) {
                            locker.wait(task.getTime() - curTime);
                        }
                    } else {
                        // 時(shí)間到了, 執(zhí)行這個(gè)任務(wù)
                        task.run();
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        t.start();
    }
}

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