1 private List<User> users = Arrays.asList(
2 new User("1001", "John", 16),
3 new User("1002", "Carly", 17),
4 new User("1003", "Tom", 11),
5 new User("1004", "Mike", 11));
6
7
8 private void lambdaFunctions() {
9
10 // 转为某一属性的集合
11 List<String> names = users.stream().map(User::getName).collect(Collectors.toList());
12
13 // 转为以某一属性为key,另一属性为value的map
14 Map<String, Integer> idAgeMap = users.stream().collect(Collectors.toMap(User::getId, User::getAge));
15
16 // 转为以某一属性为key,对象本身为value的map
17 Map<String, User> idUserMap = users.stream().collect(Collectors.toMap(User::getId, User -> User));
18
19 // 转为以某一属性为key,对象本身的集合为value
20 Map<String, List<User>> idUsersMap = users.stream().collect(Collectors.groupingBy(User::getId, Collectors.toList()));
21
22 // 过滤
23 List<User> users1 = users.stream().filter(user -> user.getAge() >= 16).collect(Collectors.toList());
24
25 //过滤
26 List<User> users2 = users.stream().filter(user -> {
27 return user.getAge() < 16;
28 }).collect(Collectors.toList());
29
30
31 // A对象集合转为B对象集合
32 List<Person> persons = users.stream().map(user -> {
33 return new Person(user.getId(), user.getName(), user.getAge());
34 }).collect(Collectors.toList());
35
36
37 }
