淘宝面试题之CountDownLatch应用_countdownlatch的面试题-优快云博客

本文链接：https://blog.youkuaiyun.com/lyzx_in_csdn/article/details/78710592

本文深入探讨了在淘宝面试中常见的CountDownLatch应用场景，通过实例解析其使用方法和关键特性，帮助读者理解如何在多线程环境中协调任务执行。

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package com.lyzx.day01;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;

/**
* 曾经的面试题：（淘宝？）
* 实现一个容器，提供两个方法 add,size
* 写两个线程，线程1添加10个元素到容器中，线程2实现监控元素的个数，当个数到5个时，线程2给出提示并结束
*
*/
public class T5{
    public static void main(String[] args) {
        CountDownLatch latch = new CountDownLatch(1);
        Arr<Object> arr = new Arr<Object>(latch);

        new Thread(new R2(latch)).start();
        new Thread(new R1(arr)).start();
    }
}

class Arr<E>{
    private CountDownLatch latch;
    private List<E> arr = new ArrayList<E>();

    public Arr(CountDownLatch latch){
        this.latch=latch;
    }

    public synchronized boolean add(E e){
        boolean v = arr.add(e);
        try {
            Thread.sleep(300);
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }

        if(5 == size()){
            latch.countDown();
        }
        System.out.println("======"+size());
        return v;
    }

    public synchronized int size(){
        return arr.size();
    }
}

class R1 implements Runnable{
    private Arr<Object> arr;
    public R1(Arr<Object> arr){
        this.arr=arr;
    }

    @Override
    public void run(){
        for(int i=0;i<10;i++){
            arr.add(new Object());
        }
    }
}

class R2 implements Runnable{
    private CountDownLatch latch;

    public R2(CountDownLatch latch){
        this.latch= latch;
    }

    @Override
    public void run(){
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("now 。。。。。over..");
    }
}