java8 lambda小试牛刀，利用Stream把list转map,并将两个list的数据对象合并起来

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1. public static void main(String[] args) {  
2.         // 集合1  
3.         List<SkillUpgrade> lists = new ArrayList<>();  
4.         SkillUpgrade s = new SkillUpgrade();  
5.         s.setLv(1);  
6.         s.setAppearNum(100);  
7.         lists.add(s);  
8.         SkillUpgrade s2 = new SkillUpgrade();  
9.         s2.setLv(2);  
10.         s2.setAppearNum(200);  
11.         lists.add(s2);  
12.         // 集合1  
13.         List<SkillUpgrade> listx = new ArrayList<>();  
14.         SkillUpgrade x = new SkillUpgrade();  
15.         x.setLv(1);  
16.         x.setSelectNum(1100);  
17.         listx.add(x);  
18.         SkillUpgrade x2 = new SkillUpgrade();  
19.         x2.setLv(2);  
20.         x2.setSelectNum(1200);  
21.         listx.add(x2);  
22.         // 把list转map,{k=lv,vaule=并为自身}  . SkillUpgrade->SkillUpgrade或Function.identity()  
23.         Map<Integer, SkillUpgrade> map = listx.stream()  
24.                 .collect(Collectors.toMap(SkillUpgrade::getLv, SkillUpgrade -> SkillUpgrade));  
25.         System.out.println(“map:=”+map);  
26.         // 合并  
27.         lists.forEach(n -> {  
28.             // 如果等级一致  
29.             if (map.containsKey(n.getLv())) {  
30.                 SkillUpgrade obj = map.get(n.getLv());  
31.                 // 把数量复制过去  
32.                 n.setSelectNum(obj.getSelectNum());  
33.             }  
34.         });  
35.         System.out.println(“lists:=”+lists);  
36.         // 重复问题  
37.         Map<Integer, SkillUpgrade> keyRedo = listx.stream()  
38.                 .collect(Collectors.toMap(SkillUpgrade::getLv, Function.identity(), (key1, key2) -> key2));  
39.         // 方式二：指定实例的map  
40.         Map<Integer, SkillUpgrade> linkedHashMap = listx.stream().collect(Collectors.toMap(SkillUpgrade::getLv,  
41.                 SkillUpgrade -> SkillUpgrade, (key1, key2) -> key2, LinkedHashMap::new));  
42.     }  
43.       
44.     /** 
45.      * output:map:={1=SkillUpgrade [skillId=null, skillName=null, lv=1, persNum=null, selectNum=1100, appearNum=null], 2=SkillUpgrade [skillId=null, skillName=null, lv=2, persNum=null, selectNum=1200, appearNum=null]} 
46.      *        lists:=[SkillUpgrade [skillId=null, skillName=null, lv=1, persNum=null, selectNum=1100, appearNum=100], SkillUpgrade [skillId=null, skillName=null, lv=2, persNum=null, selectNum=1200, appearNum=200]] 
47.      */  

输出结果：

map:={1=SkillUpgrade [skillId=null, skillName=null, lv=1, persNum=null, selectNum=1100, appearNum=null], 2=SkillUpgrade [skillId=null, skillName=null, lv=2, persNum=null, selectNum=1200, appearNum=null]}
lists:=[SkillUpgrade [skillId=null, skillName=null, lv=1, persNum=null, selectNum=1100, appearNum=100], SkillUpgrade [skillId=null, skillName=null, lv=2, persNum=null, selectNum=1200, appearNum=200]]