java根据对象的日期格式的字段进行降序排序

妖狐艹你老母 2022-08-25 14:00 188阅读 0赞

首先应用到java util工具类中的Comparator<T>接口的方法：

compare(Object o1,Object o2)方法是java.util.Comparator<T>接口的方法，它实际上用的是待比较对象的compareTo(Object o)方法。

具体实例：

User对象：

import java.io.Serializable;
    import java.util.Date;
    
    /**
     * @author wangmuming
     * 
     */
    public class User implements Comparable<Object>, Serializable {
    
    	/**
    	 * 
    	 */
    	private static final long serialVersionUID = 1L;
    
    	private int id;
    
    	private String name;
    
    	private Date birthday;
    
    	public User(int id, String name, Date birthday) {
    		this.id = id;
    		this.name = name;
    		this.birthday = birthday;
    	}
    
    	/*
    	 * Getters and Setters
    	 */
    	public int getId() {
    		return id;
    	}
    
    	public void setId(int id) {
    		this.id = id;
    	}
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	public Date getBirthday() {
    		return birthday;
    	}
    
    	public void setBirthday(Date birthday) {
    		this.birthday = birthday;
    	}
    
    	@Override
    	public int compareTo(Object o) {
    		if (this == o) {
    			return 0;
    		} else if (o != null && o instanceof User) {
    			User u = (User) o;
    			if (u.getBirthday().getTime() < this.birthday.getTime()) //根据date进行排序
    				return -1;
    			else
    				return 1;
    			// if (id <= u.id) { //根据id进行排序
    			// return -1;
    			// } else {
    			// return 1;
    			// }
    		} else {
    			return -1;
    		}
    	}
    	
    	@Override
    	public String toString() {
    		return "user is: id :"+this.id + "|  name :"+this.name +"| birthday :"+this.birthday.toLocaleString();
    	}

测试方法：

import java.util.ArrayList;
    import java.util.Collections;
    import java.util.Comparator;
    import java.util.Date;
    
    public class Test{
        //编写Comparator,根据User的birthday对User进行排序
        private static final Comparator<User> COMPARATOR = new Comparator<User>() {
           public int compare(User o1, User o2) {
               return o1.compareTo(o2);//运用User类的compareTo方法比较两个对象       
          }
       };
        
        public static void main(String[] args) {
            ArrayList<User> user = new ArrayList<User>();
            User user1 = new User(1,"wangmm1",new Date());
            User user3 = new User(2,"wangmm2",new Date(new Date().getTime()+20000));
            User user2 = new User(3,"wangmm3",new Date(new Date().getTime()+10000));
            User user4 = new User(4,"wangmm3",new Date(new Date().getTime()+50000));
            user.add(user2);
            user.add(user1);
            user.add(user3);
            user.add(user4);
          
        
            Collections.sort(user, COMPARATOR);//用我们写好的Comparator对user进行排序
            for(int i=0;i<user.size();i++){
            	System.out.println(user.get(i).toString());
            }
        }

执行结果：