这个怎么按照年龄大小升序排列啊

Question

这个排序的不会排了，是用抽象类与接口的知识嘛，怎么排列呀，谢谢啦

Answer 1

第一种方法，User实现Comparable接口，重写compareTo方法，排序则可以使用Collections.sort

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        //定义一组User数据
        List<User> userList = new ArrayList<>();
        User user = new User("1","c",12);
        userList.add(user);
        user = new User("2","b",20);
        userList.add(user);
        user = new User("3","a",12);
        userList.add(user);
        
        //排序
        Collections.sort(userList);
        //输出
        System.out.println(userList);
    }
}

class User implements Comparable{
    public String id;
    public String name;
    public int age;

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

    @Override
    public int compareTo(Object o) {
        User user = (User)o;
        if(this.age == user.age){
            //年龄相同，则按姓名排序
            return this.name.compareTo(user.name);
        }
        //年龄不相同，升序排列
        return this.age - user.age;
    }

    @Override
    public String toString() {
        return "User{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

第二种，User可以不实现Comparable接口，改成在Collections.sort里面实现Comparator接口的compare方法

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        //定义一组User数据
        List<User> userList = new ArrayList<>();
        User user = new User("1", "c", 12);
        userList.add(user);
        user = new User("2", "b", 20);
        userList.add(user);
        user = new User("3", "a", 12);
        userList.add(user);

        //排序
        Collections.sort(userList, new Comparator<User>() {
            @Override
            public int compare(User o1, User o2) {
                if (o1.age == o2.age) {
                    //年龄相同，则按姓名排序
                    return o1.name.compareTo(o2.name);
                }
                //年龄不相同，升序排列
                return o1.age - o2.age;
            }
        });

        //输出
        System.out.println(userList);
    }
}

class User {
    public String id;
    public String name;
    public int age;

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

    @Override
    public String toString() {
        return "User{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}