集合List根據多個字段進行排序

需求：List集合按照多個字段進行排序

首先得讓排序的實體類實作Comparable類并且重寫它的compareTo方法，在compareTo中你可以自定義排序的規則。如果前者大于後者，則傳回1，若果相等則傳回0，若果前者小于後者，則傳回-1；String字元串比較的時候也會經常用到這個compareTo方法，檢視String類，可以看到它也實作了Comparable類。

建立一個User類：按照id升序，age降序來排序。

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;
            }
        }
    }
    
}
           

再建一個Junit測試類

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("排序後：");
        //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("");
    }

}
           

排序結果

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