并发编程学习案例-模拟抢红包

news2024/9/27 15:28:16

一、前言

再来系统动手学习一下Java并发编程。
知识点：CountDownLatch 的发令枪使用模式；红包均分，最后一个分不完的解决方法
抢红包的需求,每个红包均分，最后一个除外
1. 设置红包总额
2. 设置红包的个数
3. 模拟抢红包的人数（细节：涉及余额分配 10元3个人抢，得把钱分完）
4. 抢红包，同一时间多个人可以同时开始（细节：要保证同时开始）

二、代码案例

package com.lvzb.concurrent;

import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.Test;

import java.util.Scanner;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * 抢红包案例
 *
 * @author: lvzb31988
 * @date: 2023/01/09 20:00
 */
@Slf4j
public class GrabRedEnvelopeTest {

    public static void main(String[] args) throws InterruptedException {

        int totalAmount;
        int num;
        int peopleNum;
        CountDownLatch countDownLatch = new CountDownLatch(1);
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入红包金额：");
        totalAmount = scanner.nextInt();
        System.out.println("请输入拆分多少个红包：");
        num = scanner.nextInt();
        System.out.println("请输入多少个人抢：");
        peopleNum = scanner.nextInt();
        RedEnvelope redEnvelope = new RedEnvelope(totalAmount, num, countDownLatch);

//        for (int i = 1; i <= peopleNum; i++) {
//            new Thread(redEnvelope, "第" + i + "个人").start();
//        }
//        countDownLatch.countDown();

        ExecutorService pool = Executors.newFixedThreadPool(peopleNum);
        for (int i = 1; i <= peopleNum; i++) {
            pool.execute(redEnvelope);
        }
        countDownLatch.countDown();
        // 不关闭池的话，程序不会结束
        pool.shutdown();
    }

    /**
     * 抢红包的需求,每个红包均分，最后一个除外
     * 1. 设置红包总额
     * 2. 设置红包的个数
     * 3. 模拟抢红包的人数 （细节：涉及余额分配 10元3个人抢，得把钱分完）
     * 4. 抢红包，同一时间多个人可以同时开始 （细节：要保证同时开始）
     */
    public static class RedEnvelope implements Runnable {
        /**
         * 红包总额
         */
        private int totalAmount;
        /**
         * 红包个数
         */
        private int num;
        /**
         * 每个红包均分的 额度
         */
        private int eachAmount;
        /**
         * 特殊处理最后一个红包的额度，防止分不完
         */
        private int lastAmount;

        // countDownLatch 的发令枪模式
        private CountDownLatch countDownLatch;
        // 保证线程安全
        private Object lock = new Object();

        public RedEnvelope(int totalAmount, int num, CountDownLatch countDownLatch) {
            this.totalAmount = totalAmount;
            this.num = num;
            this.countDownLatch = countDownLatch;
            this.eachAmount = totalAmount / num;
            // 最后一个红包金额 =  总额 - （红包总数-1）* 每个红包的数
            this.lastAmount = totalAmount - (num - 1) * eachAmount;
        }

        @Override
        public void run() {
            synchronized (lock) {
                try {
                    countDownLatch.await();
                } catch (InterruptedException e) {
                    // 如果当前线程异常，就可以通知线程应该中断了
                    Thread.currentThread().interrupt();
                    e.printStackTrace();
                }
                int currentAmount;
                if (num != 1) {
                    currentAmount = eachAmount;
                } else {
                    currentAmount = lastAmount;
                }
                if (num > 0) {
                    num--;
                    System.out.println(Thread.currentThread().getName() + ": hhhh 我抢到了" + currentAmount + "元...");
                } else {
                    System.out.println(Thread.currentThread().getName() + ": 没有抢到，错过一个亿...");
                }
            }
        }
    }
}