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
*/
@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

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

来源：https://blog.csdn.net/qq_42274641/article/details/103720085