从内部列表java 8的对象列表中获取id列表

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        List<User> userList = new ArrayList<>();

        userList.add(new User(1, "张三"));
        userList.add(new User(2, "李四"));
        userList.add(new User(3, "王五"));

        List<Integer> idList = userList.stream()
                .map(User::getId)
                .collect(Collectors.toList());

        System.out.println("ID列表: " + idList);
    }

    static class User {
        private int id;
        private String name;

        public User(int id, String name) {
            this.id = id;
            this.name = name;
        }

        public int getId() {
            return id;
        }

        public String getName() {
            return name;
        }
    }
}

ID列表: [1, 2, 3]