DelayQueue理解

Posted 2020-12-08 yangfei629

一、定义

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时延队列，只要经过一段时间后才能从队列中取出。

特点：

1、无界的阻塞队列。

2、只能存放实现了Delayed接口的对象

      时延就是通过getDelay获取的，getDelay<=0时，才能取出队列中的值

3、内部使用PriorityQueue , 比较的就是时延

 

二、使用

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代码样例

public class DelayedBean implements Delayed {
    private long startTimeMills;

    private long delayMills;

    public DelayedBean(long startTimeMills, long delayMills) {
        this.startTimeMills = startTimeMills;
        this.delayMills = delayMills;
    }

    @Override
    public long getDelay(TimeUnit unit) {
        return unit.convert((startTimeMills+delayMills) - System.currentTimeMillis(),TimeUnit.MILLISECONDS);
    }

    @Override
    public int compareTo(Delayed object) {
        DelayedBean descObject = (DelayedBean) object;
        return (int)Long.compare(this.getDelay(TimeUnit.MILLISECONDS),descObject.getDelay(TimeUnit.MILLISECONDS));
    }

    @Override
    public String toString() {
        return "DelayedBean{" +
                "startTimeMills=" + startTimeMills +
                ", delayMills=" + delayMills +
                ‘}‘;
    }

    public static void main(String[] args) throws InterruptedException {
        DelayQueue<DelayedBean> delayQueue = new DelayQueue<>();
        delayQueue.offer(new DelayedBean(System.currentTimeMillis(),1000));
        delayQueue.offer(new DelayedBean(System.currentTimeMillis(),2000));
        Thread.sleep(1000);
        System.out.println("first get from delayqueue="+delayQueue.poll());
        System.out.println("second get from delayqueue="+delayQueue.poll());
    }
}

 

输出：

first get from delayqueue=DelayedBean{startTimeMills=1591628168555, delayMills=1000}
second get from delayqueue=null

 

可见第一个元素达到了时延1000ms , 故可以取出

第二个元素为达到时延2000ms,故取不出返回null