class DelayedTask implements Runnable, Delayed { // Delayed接口必須實(shí)現(xiàn)，Runnable接口可以不實(shí)現(xiàn)
    private static int counter = 0;
    private final int id = counter++;
    /**
     * 延遲的時(shí)間(單位: 毫秒)
     */
    private final int delta;
    /**
     * 任務(wù)準(zhǔn)備執(zhí)行的時(shí)間點(diǎn)(單位: 納秒)
     */
    private final long trigger;
    protected static List<DelayedTask> sequence = new ArrayList<>();
    public DelayedTask(int delayInMilliseconds) {
        delta = delayInMilliseconds;
        trigger = System.nanoTime() + NANOSECONDS.convert(delta, MILLISECONDS);
        sequence.add(this);
    }
    @Override
    public long getDelay(@NotNull TimeUnit unit) {
        // 過期時(shí)間
        return unit.convert(trigger - System.nanoTime(), NANOSECONDS);
    }
    /**
     * 用于在過期任務(wù)隊(duì)列中，任務(wù)之間執(zhí)行順序的排序
     */
    @Override
    public int compareTo(@NotNull Delayed arg) {
        DelayedTask that = (DelayedTask)arg;
        if(trigger < that.trigger) return -1;
        if(trigger > that.trigger) return 1;
        return 0;
    }
    @Override
    public void run() {
        System.out.println(this + " ");
    }
    @Override
    public String toString() {
        // 語法規(guī)則： %[argument_index$][flags][width][.precision]conversion
        // %后面的1$指的是第一個(gè)參數(shù)，也就是delta
        // $后面的-4d指的是如果數(shù)據(jù)總長度不夠4位，則由右向左補(bǔ)足空格
        return String.format("[%1$-4d]", delta) + " Task " + id;
    }
    public String summary() {
        return "(" + id + ":" + delta + ")";
    }
    public static class EndSentinel extends DelayedTask {
        private ExecutorService exec;
        public EndSentinel(int delay, ExecutorService e) {
            super(delay);
            exec = e;
        }
        @Override
        public void run() {
            for(DelayedTask pt : sequence) {
                System.out.println(pt.summary() + " ");
            }
            System.out.println();
            System.out.println(this + " Calling shutdownNow()");
            exec.shutdownNow();
        }
    }
}

class DelayedTaskConsumer implements Runnable {
    private DelayQueue<DelayedTask> q;
    public DelayedTaskConsumer(DelayQueue<DelayedTask> q) {
        this.q = q;
    }
    @Override
    public void run() {
        try {
            while(!Thread.interrupted()) {
                // DelayQueue take()
                // 取出隊(duì)列中的head元素，若隊(duì)列中沒有任何延遲到期的元素存在，則該方法將會(huì)被阻塞
                // 此時(shí)有兩種可能: 1. 隊(duì)列中沒有元素 2. 隊(duì)列中有元素，但都尚未過期
                // 直到隊(duì)列中有延遲到期的元素為止
                // 即便是不讓DelayedTask實(shí)現(xiàn)Runnable接口，本例的執(zhí)行結(jié)果也不會(huì)發(fā)生改變。
                // 因?yàn)榇颂幹苯诱{(diào)用了run()方法，并沒有分配其他線程去驅(qū)動(dòng)DelayedTask
                q.take().run();
            }
        } catch (InterruptedException e) {
            // Acceptable way to exit
            System.out.println("Acceptable way to exit");
        }
        System.out.println("Finished DelayedTaskConsumer");
    }
}

public class DelayQueueDemo {
    public static void main(String[] args) {
        test2();
    }
    public static void test1() {
        Random random = new Random(47);
        ExecutorService exec = Executors.newCachedThreadPool();
        DelayQueue<DelayedTask> queue = new DelayQueue<>();
        // Fill with tasks that have random delays:
        for(int i = 0; i < 5; i++) {
            queue.put(new DelayedTask(random.nextInt(5000)));
        }
        //使用DelayQueue take()的方式獲取任務(wù)
        queue.add(new DelayedTask.EndSentinel(5000, exec));
        exec.execute(new DelayedTaskConsumer(queue));
    }
    public static void test2() {
        Random random = new Random(47);
        ExecutorService exec = Executors.newCachedThreadPool();
        DelayQueue<DelayedTask> queue = new DelayQueue<>();
        // Fill with tasks that have random delays:
        for(int i = 0; i < 5; i++) {
            queue.put(new DelayedTask(random.nextInt(5000)));
        }
        //使用DelayQueue poll()方式獲取任務(wù)
        while(queue.size() != 0) {
            // 每執(zhí)行一次DelayQueue poll()且返回的元素不是null，則DelayQueue等待隊(duì)列的元素個(gè)數(shù)會(huì)減一
            DelayedTask task = queue.poll();
            if(task != null) {
                System.out.println(LocalDateTime.now(ZoneId.of("+08:00")));
            }
        }
    }
}