java8 如何实现分组计算数量和计算总数_Java教程

java8 如何实现分组计算数量和计算总数

2021-09-28 09:52FanClys Java教程

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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);

									});