JAVA JDK8 List分组的实现和用法

概述

对list进行分组是日常开发中，经常遇到的，在jdk 8中对list按照某个属性分组的代码，超级简单。

package test;

import com.alibaba.fastjson.json;

import com.alibaba.fastjson.serializer.serializerfeature;

import java.util.arraylist;

import java.util.list;

import java.util.map;

import java.util.stream.collectors;

public class listgrouptest {

public static void main(string[] args) {

list<coupon> couponlist = new arraylist<>();

coupon coupon1 = new coupon(1,100,"优惠券1");

coupon coupon2 = new coupon(2,200,"优惠券2");

coupon coupon3 = new coupon(3,300,"优惠券3");

coupon coupon4 = new coupon(3,400,"优惠券4");

couponlist.add(coupon1);

couponlist.add(coupon2);

couponlist.add(coupon3);

couponlist.add(coupon4);

map<integer, list<coupon>> resultlist = couponlist.stream().collect(collectors.groupingby(coupon::getcouponid));

system.out.println(json.tojsonstring(resultlist, serializerfeature.prettyformat));

}

package test;

public class coupon {

private integer couponid;

private integer price;

private string name;

public coupon(integer couponid, integer price, string name) {

this.couponid = couponid;

this.price = price;

this.name = name;

}

public integer getcouponid() {

return couponid;

}

public void setcouponid(integer couponid) {

this.couponid = couponid;

}

public integer getprice() {

return price;

}

public void setprice(integer price) {

this.price = price;

}

public string getname() {

return name;

}

public void setname(string name) {

this.name = name;

}

上面的例子是对list按照couponid分组，couponid一样的，归为一组。打印结果如下：

{
1:[
{
"couponid":1,
"name":"优惠券1",
"price":100
}
],
2:[
{
"couponid":2,
"name":"优惠券2",
"price":200
}
],
3:[
{
"couponid":3,
"name":"优惠券3",
"price":300
},
{
"couponid":3,
"name":"优惠券4",
"price":400
}
]
}

如果分组后，分组内并不想是对象，而是对象的属性，也可以做到的。

JAVA JDK8 List分组的实现和用法

相关文章

快网idc优惠网

相关文章

微信

快网idc优惠网

QQ交流群