概述
在java jdk8 list分組的實(shí)現(xiàn)和用法一文中介紹了jdk 8如何對(duì)list進(jìn)行分組，但是沒有提到如何在分組后，獲取每個(gè)分組的第一個(gè)元素。其實(shí)這個(gè)也很簡(jiǎn)單，代碼如下：
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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 listgroupfindfirsttest3 { public static void main(string[] args) { list<coupon> couponlist = new arraylist<>(); coupon coupon1 = new coupon(1,100,"優(yōu)惠券1"); coupon coupon2 = new coupon(2,200,"優(yōu)惠券2"); coupon coupon3 = new coupon(3,300,"優(yōu)惠券3"); coupon coupon4 = new coupon(3,400,"優(yōu)惠券4"); couponlist.add(coupon1); couponlist.add(coupon2); couponlist.add(coupon3); couponlist.add(coupon4); map<integer, coupon> resultlist = couponlist.stream().collect(collectors.groupingby(coupon::getcouponid,collectors.collectingandthen(collectors.tolist(),value->value.get(0)))); system.out.println(json.tojsonstring(resultlist, serializerfeature.prettyformat)); }} |
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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; }} |
需要借助collectors.collectingandthen方法，對(duì)組內(nèi)的元素進(jìn)行處理，這里是獲取第一個(gè)元素。
代碼輸出結(jié)果如下：
{ 1:{
"couponid":1,
"name":"優(yōu)惠券1",
"price":100
},
2:{
"couponid":2,
"name":"優(yōu)惠券2",
"price":200
},
3:{
"couponid":3,
"name":"優(yōu)惠券3",
"price":300
}
}
總結(jié)
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原文鏈接：https://blog.csdn.net/linsongbin1/article/details/84112877
