list轉map Java Stream的使用

一、list ->map

1、有如下表對應表結構，實現

2、先進行一些簡單的操作

定義類

private integer rank;  

private string description; 
public movie(integer rank, string description) 
public integer getrank() 
public string getdescription() 
@override
public string tostring() 

直接遍歷將對應值put放入map

//建立乙個 listmovies

listmovies = new arraylist(); 
movies.add(new movie(1, "the shawshank redemption")); 
movies.add(new movie(2, "the godfather")); 
for (movie movie : movies) 
//列印map
int rank=entry.getkey();
movie movie=entry.getvalue();
system.out.println(rank+":"+movie);
}

//建立乙個list

listmovies = new arraylist(); 
movies.add(new movie(1, "the shawshank redemption")); 
movies.add(new movie(2, "the godfather"));

listranklist=movies.stream().map(p->p.getrank()).collect(collectors.tolist());

3、回到問題

listredbaggoodslist --->  listsusnapids 即：redbaggoods的ids(redbaggoodslist)獲取susnapinfo表的ids

listsusnapids = redbaggoodslist.stream().map(p->p.getsusnapid()).collect(collectors.tolist());

listgiftstatuslist = redbaggoodslist.stream().map(p -> p.getgiftstatus()).distinct().collect(collectors.tolist());

map> redbagid2redbagmap = redbaglist.stream().collect(collectors.groupingby(p->p.getredbagid()));

long sucount = susnapinfolist.stream().map(p->p.getsuname()).distinct().count();

listgiftids = redbaggoodslist.stream().map(p -> p.getgiftbagid()).filter(p -> p.equals(firstgiftids))

.collect(collectors.tolist());

比較簡單，只給出**

// 集合去重

listls1 = new arraylist<>();
ls1.add("a");
ls1.add("b");
ls1.add("c");
listls2 = new arraylist<>();
ls2.add("a");
ls2.add("b");
ls2.add("c");
ls2.add("d");
// 是否存在ls1完全包含ls2的情況
boolean exist = ls1.containsall(ls2);
if (!exist) 
system.out.println(ls2);// d

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