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JDK8中对List按照某个属性分组的代码，超级简单。
packagetest;
importcom.alibaba.fastjson.JSON;
importcom.alibaba.fastjson.serializer.SerializerFeature;
importjava.util.ArrayList;
importjava.util.List;
importjava.util.Map;
importjava.util.stream.Collectors;
publicclassListGroupTest{
publicstaticvoidmain(String[]args){
ListcouponList=newArrayList<>();
Couponcoupon1=newCoupon(1,100,"优惠券1");
Couponcoupon2=newCoupon(2,200,"优惠券2");
Couponcoupon3=newCoupon(3,300,"优惠券3");
Couponcoupon4=newCoupon(3,400,"优惠券4");
couponList.add(coupon1);
couponList.add(coupon2);
couponList.add(coupon3);
couponList.add(coupon4);
Map>resultList=couponList.stream().collect(Collectors.groupingBy(Coupon::getCouponId));
System.out.println(JSON.toJSONString(resultList,SerializerFeature.PrettyFormat));
}
}
packagetest;
publicclassCoupon{
privateIntegercouponId;
privateIntegerprice;
privateStringname;
publicCoupon(IntegercouponId,Integerprice,Stringname){
this.couponId=couponId;
this.price=price;
this.name=name;
}
publicIntegergetCouponId(){
returncouponId;
}
publicvoidsetCouponId(IntegercouponId){
this.couponId=couponId;
}
publicIntegergetPrice(){
returnprice;
}
publicvoidsetPrice(Integerprice){
this.price=price;
}
publicStringgetName(){
returnname;
}
publicvoidsetName(Stringname){
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。
packagetest;
importcom.alibaba.fastjson.JSON;
importcom.alibaba.fastjson.serializer.SerializerFeature;
importjava.util.ArrayList;
importjava.util.List;
importjava.util.Map;
importjava.util.stream.Collectors;
publicclassListGroupTest2{
publicstaticvoidmain(String[]args){
ListcouponList=newArrayList<>();
Couponcoupon1=newCoupon(1,100,"优惠券1");
Couponcoupon2=newCoupon(2,200,"优惠券2");
Couponcoupon3=newCoupon(3,300,"优惠券3");
Couponcoupon4=newCoupon(3,400,"优惠券4");
couponList.add(coupon1);
couponList.add(coupon2);
couponList.add(coupon3);
couponList.add(coupon4);
Map>resultList=couponList.stream().collect(Collectors.groupingBy(Coupon::getCouponId,Collectors.mapping(Coupon::getName,Collectors.toList())));
System.out.println(JSON.toJSONString(resultList,SerializerFeature.PrettyFormat));
}
}
这样分组内就是name属性了。打印结果如下：
{
1:[
"优惠券1"
],
2:[
"优惠券2"
],
3:[
"优惠券3",
"优惠券4"
]
}
总结
以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，谢谢大家对毛票票的支持。如果你想了解更多相关内容请查看下面相关链接