java8分组计算数量和计算总数
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
|
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
|
1
2
3
4
5
6
7
8
9
|
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=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
