java8 如何实现分组计算数量和计算总数

java8分组计算数量和计算总数

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 */@Datapublic 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

int[] arr=new int[]{5,1,3,4,1};//若统计的是int数组，先转化为ListList<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mapmap.forEach((k,v)->{      System.out.println("k="+k+",v="+v);});

k=1,v=2k=3,v=1k=4,v=1k=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。

无神的瞳孔，我迫切想逃离这周遭被钢筋混凝土堆架的城市，