背景
现在需要对一个有序的手机列表按照品牌进行分组，那么我们使用java8中的groupingBy的时候默认返回的是无序的Map，如果想输出有序的Map，需要使用三参数的groupingBy，指定返回有序的LinkedHashMap。
LinkedHashMap<String,List<Mobile>> linkedHashMap = mobileList.stream().collect(Collectors.groupingBy(Mobile::getBrand, LinkedHashMap::new,Collectors.toList()));
代码如下
package com.lingyejun.blog; import java.util.Arrays; import java.util.LinkedHashMap; import java.util.List; import java.util.Map; import java.util.stream.Collectors; public class MobileMain { public static void main(String[] args) { List<Mobile> mobileList = getMobileList(); Map<String,List<Mobile>> hashMap = mobileList.stream().collect(Collectors(Mobile::getBrand)); LinkedHashMap<String,List<Mobile>> linkedHashMap = mobileList.stream().collect(Collectors.groupingBy(Mobile::getBrand, LinkedHashMap::new,Collectors.toList())); } public static List<Mobile> getMobileList() { Mobile mobile1 = new Mobile("华为Mate40","华为",1); Mobile mobile2 = new Mobile("华为Mate30","华为",2); Mobile mobile3 = new Mobile("小米MIX7","小米",3); Mobile mobile4 = new Mobile("小米11畅玩版","小米",4); Mobile mobile5 = new Mobile("小米11青春版","小米",5); Mobile mobile6 = new Mobile("Iphone11","Iphone",6); Mobile mobile7 = new Mobile("Oppo Reno6","Oppo",7); Mobile mobile8 = new Mobile("Oppo K7x","Oppo",8); return Arrays.asList(mobile1, mobile2, mobile3, mobile4, mobile5, mobile6, mobile7, mobile8); } }
原始的list是按照sequence顺序排列的
按照常规的groupingBy分组后得到的结果是无序的
Map<String,List<Mobile>> hashMap = mobileList.stream().collect(Collectors.groupingBy(Mobile::getBrand));
使用新的方式
LinkedHashMap<String,List<Mobile>> linkedHashMap = mobileList.stream().collect(Collectors.groupingBy(Mobile::getBrand, LinkedHashMap::new,Collectors.toList()));
本篇文章如有帮助到您，请给「翎野君」点个赞，感谢您的支持。
原文链接：https://www.cnblogs.com/lingyejun/p/15216333.html
