JAVA对象排序

JAVA对象主要通过实现Comparable接口的compareTo方法来定义对象排序列，代码如下：

package com.study;

public class User implements Comparable{
    private String userName;

    public User(){};
    public User(User user){
        this.userName = user.userName;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    @Override
    public int compareTo(User o) {
        return this.userName.compareTo(o.getUserName());
    }

}

调用Collections.sort(List)方法来实现对象升序排序

package com.study;

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

public class testObjextPX {

    public static void main(String[] args){
        User user1 = new User();
        user1.setUserName("zhangsan");
        User user2 = new User();
        user2.setUserName("lisi");
        List list = new ArrayList<>();
        list.add(user1);
        list.add(user2);
        Collections.sort(list);
        for(User u:list){
            System.out.println(u.getUserName());
        }
    }
}

输出结果：

lisi
zhangsan

可调用：
Collections.sort(List,Collections.reverseOrder())进行降序操作
Collections.reverse(List)进行逆序操作