List排序问题

最新推荐文章于 2021-10-05 18:09:59 发布

原创最新推荐文章于 2021-10-05 18:09:59 发布 · 708 阅读

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本文展示了如何使用Java中的Collections类和自定义比较器对包含日期和年龄信息的实体对象列表进行排序，包括实现步骤和运行结果展示。

对List中对象的某个字段按照从大到小或者从小到大的顺序进行排序

看代码：

首先创建一个实体对象：

package com.sort;


class User {
	String name;
	String age;
	String birthday;

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

	public String getAge() {
		return age;
	}

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

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getBirthday() {
		return birthday;
	}

	public void setBirthday(String birthday) {
		this.birthday = birthday;
	}

}

然后组织数据，并进行排序：

package com.sort;

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

public class SortTest {

	 
	 public static void main(String[] args){
	  List<User> userlist=new ArrayList<User>();
	  userlist.add(new User("dd","4","2015-08-01"));
	  userlist.add(new User("aa","1","2015-08-01"));
	  userlist.add(new User("ee","5","2015-08-03"));
	  userlist.add(new User("bb","1","2015-08-04"));  
	  userlist.add(new User("ff","5","2015-08-05"));
	  userlist.add(new User("cc","3","2015-08-06"));
	  userlist.add(new User("gg","6","2015-08-07"));
	  
	 //直接调用Collections中的比较器，重写compare方法即可，不需要继承Comparable接口
	  Collections.sort(userlist, new Comparator<User>(){

		@Override
		public int compare(User o1, User o2) {
			//首先比较日期大小，按照降序排列，如果要按照升序排列，只需修改成：
			//int flag = o1.birthday.compareTo(o2.birthday);
			int flag = o2.birthday.compareTo(o1.birthday);
			if(flag==0){
				//如果日期一致，则比较年龄大小按照升序排列
				return o1.age.compareTo(o2.age);
			}
			return flag;
		}
		  
	  });
	   
	  for (int i=0;i<userlist.size();i++){
	   User user_temp=(User)userlist.get(i);
	      System.out.println(user_temp.getAge()+","+user_temp.getName()+","+user_temp.birthday); 
	  }
	  
	 }
	}

运行结果

6,gg,2015-08-07
3,cc,2015-08-06
5,ff,2015-08-05
2,bb,2015-08-04
5,ee,2015-08-03
1,aa,2015-08-01
4,dd,2015-08-01