DelayQueue

/**
 *    DelayQueue 底层包含一个PriorityQueue。
 *    向DelayQueue插入的元素必须实现delay接口，DelayQueue是不边界的
 *   只有当队列中的元素过期了，即getDalay方法返回值小于0，元素才可以取出来
 *   当元素过期了不取出来，不会被删除，元素仍然在队列里
 */
public class DelayQueueTest {


    public static void main(String[] args) throws InterruptedException {
        DelayQueue<Element<String>> queue = new DelayQueue<Element<String>>();
        queue.put(new Element<>("hello1", 3000));
        long start = System.currentTimeMillis();
        System.out.println("=========");
        // TimeUnit.SECONDS.sleep(5);  //验证元素过期了不取出来，不会被删除
        queue.take();
        System.out.println(System.currentTimeMillis()-start);
    }



    static  class  Element<E>   implements Delayed{

        final  E e;

        long expireTime;
        Element (E e , long  expireTime){
            this.e = e;
            this.expireTime = System.currentTimeMillis() + expireTime;
        }


        @Override
        public long getDelay(TimeUnit unit) {
            return expireTime - System.currentTimeMillis();
        }

        @Override
        public int compareTo(Delayed o) {
            Element that = (Element) o;
            if(this.expireTime < that.expireTime){
                return  -1;
            }else if(this.expireTime > that.expireTime){
                return  1;
            }else{
                return 0;
            }
        }
    }
}