集合List根据多个字段进行排序

需求：List集合按照多个字段进行排序

首先得让排序的实体类实现Comparable类并且重写它的compareTo方法，在compareTo中你可以自定义排序的规则。如果前者大于后者，则返回1，若果相等则返回0，若果前者小于后者，则返回-1；String字符串比较的时候也会经常用到这个compareTo方法，查看String类，可以看到它也实现了Comparable类。

新建一个User类：按照id升序，age降序来排序。

package com.entity;
public class User implements Comparable<User>{
    private int id;
    private int age;
    private String name;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    
    public User(int id, int age, String name) {
        super();
        this.id = id;
        this.age = age;
        this.name = name;
    }
    @Override
    public int compareTo(User o) {
        // TODO Auto-generated method stub
        if(this.getId()>o.getId())
        {
            return 1;
        }else if(this.getId()<o.getId()){
            return -1;
        }else{
            if(this.getAge()>o.getAge()){
                return -1;
            }else{
                return 1;
            }
        }
    }
    
}

再建一个Junit测试类

package com.test;
import java.util.ArrayList;
import java.util.Collections;
import org.junit.Test;
import com.entity.User;
public class TestJunit {
    @Test
    public void test() {
        User u1=new User(1, 1, "A");
        User u2=new User(3, 2, "B");
        User u3=new User(3, 3, "C");
        User u4=new User(5, 4, "D");
        User u5=new User(5, 5, "E");
        ArrayList<User> list=new ArrayList<User>();
        list.add(u2);
        list.add(u5);
        list.add(u3);
        list.add(u4);
        list.add(u1);
        System.out.println("排序前：");
        for(int i=0;i<list.size();i++)
        {
            System.out.println("id："+list.get(i).getId() +" age:"+list.get(i).getAge() +"  name:"+list.get(i).getName());
        }
        System.out.println("排序后：");
        //id升序，age降序排序
        Collections.sort(list);
        for(int i=0;i<list.size();i++)
        {
            System.out.println("id："+list.get(i).getId() +" age:"+list.get(i).getAge() +"  name:"+list.get(i).getName());
        }
        System.out.println("");
    }

}

排序结果

原文见: https://www.jianshu.com/p/e71b8710ce0c