java8 如何实现分组计算数量和计算总数

时间:2022-09-23 11:31:41

java8分组计算数量和计算总数

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package com.pig4cloud.pigx.admin.api.vo;
import lombok.Builder;
import lombok.Data;
import lombok.experimental.Tolerate;
import java.util.*;
import java.util.stream.Collectors;
/***
 *
 *Create by 范春宇 on 2019/12/26 17:22
 */
@Data
public class RealSkuVo implements Cloneable{
    private String realEan;
    private Integer realQty;
    public static void main(String[] args) throws CloneNotSupportedException {
        List<RealSkuVo> list = new ArrayList<>();
        RealSkuVo a = new RealSkuVo();
        RealSkuVo b1 = (RealSkuVo)a.clone();
        b1.setRealEan("asdasda");
        b1.setRealQty(1);
        RealSkuVo b2 = (RealSkuVo)a.clone();
        b2.setRealEan("asdasda2");
        b2.setRealQty(1);
        RealSkuVo b3 = (RealSkuVo)a.clone();
        b3.setRealEan("asdasda3");
        b3.setRealQty(1);
        RealSkuVo b4 = (RealSkuVo)a.clone();
        b4.setRealEan("asdasda3");
        b4.setRealQty(1);
        list.add(b1);
        list.add(b2);
        list.add(b3);
        list.add(b4);
        Map<String, LongSummaryStatistics> collect = list.stream().collect(Collectors.groupingBy(RealSkuVo::getRealEan,Collectors.summarizingLong(RealSkuVo::getRealQty)));
        Map<String, Long> collect1 = list.stream().collect(Collectors.groupingBy(RealSkuVo::getRealEan, Collectors.counting()));
        System.out.println(collect);
    }
}

Java8利用Stream分组统计List(或数组)中元素的个数,结果存放在Map

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int[] arr=new int[]{5,1,3,4,1};
//若统计的是int数组,先转化为List
List<Integer> list= Arrays.stream(arr).boxed().collect(Collectors.toList());
//groupingBy分组
Map<Integer, Long> map = list.stream().collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
//控制台输出map
map.forEach((k,v)->{
      System.out.println("k="+k+",v="+v);
});

k=1,v=2
k=3,v=1
k=4,v=1
k=5,v=1

以上为个人经验,希望能给大家一个参考,也希望大家多多支持服务器之家。

原文链接:https://blog.csdn.net/qq_42274641/article/details/103720085