stream 里面的 Collectors.toMap 用法 ； list转map

https://blog.youkuaiyun.com/jiangpingjiangping/article/details/76474010

第一步：

[java] view plain copy

1. packagetest;

2. publicclassPerson{

3. privateIntegerid;

4. privateStringname;

5. publicPerson(Integerid,Stringname){

6. this.id=id;

7. this.name=name;

8. }

9. publicIntegergetId(){

10. returnid;

11. }

12. publicvoidsetId(Integerid){

13. this.id=id;

14. }

15. publicStringgetName(){

16. returnname;

17. }

18. publicvoidsetName(Stringname){

19. this.name=name;

20. }

21. }

第二步：

[java] view plain copy

1. packagetest;

2. importjava.util.ArrayList;

3. importjava.util.List;

4. importjava.util.Map;

5. importjava.util.function.Function;

6. importjava.util.stream.Collectors;

7. importjava.util.stream.Stream;

8. publicclassTest{

9. publicstaticvoidmain(String[]args){

10. Listlist=newArrayList();

11. list.add(newPerson(1,“haha”));

12. list.add(newPerson(2,“rere”));

13. list.add(newPerson(3,“fefe”));

14. Map<Integer,Person>mapp=list.stream().collect(Collectors.toMap(Person::getId,Function.identity()));

15. System.out.println(mapp);

16. System.out.println(mapp.get(1).getName());

17. Map<Integer,String>map=list.stream().collect(Collectors.toMap(Person::getId,Person::getName));

18. System.out.println(map);

19. }

20. }

得到的结果：

{1=test.Person@4b9385, 2=test.Person@1311334, 3=test.Person@2a0b20}

haha

{1=haha, 2=rere, 3=fefe}