Demo1：id归类到同一组map集合

原文链接： http://www.cnblogs.com/AlanWilliamWalker/p/10822053.html

小demo：

需求：将user id归类到同一组map集合中

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

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

        User user1 = new User();
        user1.setId(1L);
        user1.setAge("12");

        User user2 = new User();
        user2.setId(2L);
        user2.setAge("13");

        User user3 = new User();
        user3.setId(2L);
        user3.setAge("15");

        userList.add(user1);
        userList.add(user2);
        userList.add(user3);



        Map<Long, List<User>> maps = new HashMap<Long, List<User>>();

        if( null != userList && !userList.isEmpty() ) {
            for ( User user:userList) {
                    if( maps.get(user.getId()) == null ) {
                        List<User> list = new ArrayList<User>();
                        list.add(user);
                        maps.put(user.getId(),list);
                    } else  {
                        List<User> list = maps.get(user.getId());
                        list.add(user);
                        maps.put(user.getId(),list);
                    }
            }
        }

        for(Map.Entry<Long, List<User>> entry:maps.entrySet()) {
            System.out.println("id:"+entry.getKey()+";value:"+entry.getValue().size()+":::::"+entry.getValue());
        }
    }

}
class User {
    private Long id;
    private String age;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" + "id=" + id + ", age='" + age + '\'' + '}';
    }
}
class B {
    private List<String> a ;
    private List<String> b ;

    public List<String> getA() {
        return a;
    }

    public void setA(List<String> a) {
        this.a = a;
    }

    public List<String> getB() {
        return b;
    }

    public void setB(List<String> b) {
        this.b = b;
    }
}

转载于:https://www.cnblogs.com/AlanWilliamWalker/p/10822053.html