public enum QueueTypeEnum {
    ARRAY_BLOCKING_QUEUE(1, "ArrayBlockingQueue"),
    LINKED_BLOCKING_QUEUE(2, "LinkedBlockingQueue"),
    DELAY_QUEUE(3, "DelayQueue"),
    PRIORITY_BLOCKING_QUEUE(4, "PriorityBlockingQueue"),
    SYNCHRONOUS_QUEUE(5, "SynchronousQueue"),
    LINKED_TRANSFER_QUEUE(6, "LinkedTransferQueue"),
    LINKED_BLOCKING_DEQUE(7, "LinkedBlockingDeque"),
    VARIABLE_LINKED_BLOCKING_QUEUE(8, "VariableLinkedBlockingQueue"),
    MEMORY_SAFE_LINKED_BLOCKING_QUEUE(9, "MemorySafeLinkedBlockingQueue");
}

public interface Delayed extends Comparable<Delayed> {

    /**
     * 返回與此對(duì)象關(guān)聯(lián)的剩余延遲（給定的時(shí)間單位）。
     * @param unit 時(shí)間單位
     * @返回剩余延遲；零值或負(fù)值表示 延遲已過期
     */
    long getDelay(TimeUnit unit);
}

//可重入同步鎖
private final transient ReentrantLock lock = new ReentrantLock();

//DelayQueue的實(shí)現(xiàn)依賴于PriorityQueue(優(yōu)先隊(duì)列)
private final PriorityQueue<E> q = new PriorityQueue<E>();

//第一個(gè)等待某個(gè)延時(shí)對(duì)象的線程，在延時(shí)對(duì)象還沒有到期時(shí)其他線程看到這個(gè)leader不為null，那么就直接wait
//主要是為了避免大量線程在同一時(shí)間點(diǎn)喚醒，導(dǎo)致大量的競(jìng)爭(zhēng)，反而影響性能
private Thread leader = null;

//條件隊(duì)列，用于wait線程
private final Condition available = lock.newCondition();

//從上面屬性就可以看出，DelayQueue采用了餓漢模式，調(diào)用構(gòu)造方法即創(chuàng)建了隊(duì)列實(shí)例
public DelayQueue() {}

/**
 * 創(chuàng)建一個(gè)DelayQueue，最初包含給定的Collection實(shí)例集合。
 * @param c 最初包含的元素集合
 */
public DelayQueue(Collection<? extends E> c) {
    this.addAll(c);
}

class MyDelay<T> implements Delayed {

    long delayTime; // 延遲時(shí)間
    long expire; // 過期時(shí)間
    T data;

    public MyDelay(long delayTime, T t) {
        this.delayTime = delayTime;
        // 過期時(shí)間 = 當(dāng)前時(shí)間 + 延遲時(shí)間
        this.expire = System.currentTimeMillis() + delayTime;
        data = t;
    }

    /**
     * 剩余時(shí)間 = 到期時(shí)間 - 當(dāng)前時(shí)間
     */
    @Override
    public long getDelay(TimeUnit unit) {
        return unit.convert(this.expire - System.currentTimeMillis(), TimeUnit.MILLISECONDS);
    }

    /**
     * 優(yōu)先級(jí)規(guī)則：兩個(gè)任務(wù)比較，時(shí)間短的優(yōu)先執(zhí)行
     */
    @Override
    public int compareTo(Delayed o) {
        long f = this.getDelay(TimeUnit.MILLISECONDS) - o.getDelay(TimeUnit.MILLISECONDS);
        return (int) f;
    }


    @Override
    public String toString() {
        return "delayTime=" + delayTime +
                ", expire=" + expire +
                ", data=" + data;
    }
}

public class DelayQueueDemo {
    static BlockingQueue<Delayed> queue = new DelayQueue();
    public static void main(String[] args) throws InterruptedException {
        queue.add(new MyDelay(8, "第一次添加任務(wù)"));
        queue.add(new MyDelay(3, "第二次添加任務(wù)"));
        queue.add(new MyDelay(5, "第三次添加任務(wù)"));

        while (!queue.isEmpty()) {
            Delayed delayed = queue.take();
            System.out.println(delayed);
        }
    }
}