1 import com.yang.test.User;
2
3 import javax.jws.soap.SOAPBinding;
4 import java.util.*;
5 import java.util.function.Function;
6 import java.util.stream.Collectors;
7
8 public class Main {
9
10 public static void main(String[] args) {
11
12 List<User> userlist = new ArrayList<>();
13 for (int i = 0; i <10; i++) {
14
15 userlist.add(new User("张三"+i,i));
16 }
17 System.out.println(getAllages(userlist).size());
18
19 System.out.println(getUser2Map(userlist));
20
21 System.out.println(getUser2MapUser(userlist));
22
23 System.out.println(getUser2MapUser2(userlist));
24
25 System.out.println(getUser2MapUser3(userlist));
26
27 }
28
29 public static List<Integer> getAllages(List<User>userlist){
30 return userlist.stream().map(user -> user.getAge()).collect(Collectors.toList());
31 }
32
33 public static Map<Integer,String> getUser2Map(List<User>userlist){
34
35 return userlist.stream().collect(Collectors.toMap(User::getAge,User::getName));
36 }
37
38 public static Map<Integer,User> getUser2MapUser(List<User>userlist){
39
40 return userlist.stream().collect(Collectors.toMap(User::getAge,User-> User));
41 }
42
43 /**
44 * 比较优雅的写法是这样的
45 * @param userlist
46 * @return
47 */
48 public static Map<Integer,User> getUser2MapUser2(List<User>userlist){
49
50 return userlist.stream().collect(Collectors.toMap(User::getAge, Function.identity()));
51 }
52
53 /**
54 * 重复key的情况下 简单的使用后者覆盖前者的
55 */
56 public static Map<Integer,User> getUser2MapUser3(List<User>userlist){
57
58 return userlist.stream().collect(Collectors.toMap(User::getAge, Function.identity(),(key1,key2)->key2));
59 }
60
61 /**
62 *指定map的具体实现
63 * @param userlist
64 * @return
65 */
66 public static Map<Integer,User> getUser2MapUser4(List<User>userlist){
67
68 return userlist.stream().collect(Collectors.toMap(User::getAge, Function.identity(),(key1,key2)->key2, LinkedHashMap::new));
69 }
70 }
