排序日期/时间对象(最新的)

Question

我正在尝试使用下面的代码按日期/时间(最新的第一个)订购日期对象.订购不正确.我认为该compareTo方法需要以不同方式实现以实现所需的排序？

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


public class DateSorter {

    public static void main(String args[]){

        List<DateObject> list = new ArrayList<DateObject>();

        DateObject d1 = new DateObject("2012-12-05" , "11:21:19");
        list.add(d1);

        d1 = new DateObject("2012-12-05" , "11:20:19");
        list.add(d1);

        d1 = new DateObject("2012-12-05" , "11:20:19");
        list.add(d1);

        d1 = new DateObject("2012-12-04" , "10:20:19");
        list.add(d1);

        d1 = new DateObject("2010-12-07" , "13:20:19");
        list.add(d1);

        d1 = new DateObject("2012-12-05" , "11:20:19");
        list.add(d1);

        Collections.sort(list);

        for(DateObject d : list){
            System.out.println(d);
        }
    }

}

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class DateObject implements Comparable<Object> {

    private String date;
    private String time;

    public DateObject(String date, String time) {
        this.date = date;
        this.time = time;
    }

    public int compareTo(Object o) {

        DateFormat formatter;
        Date date1 = null;
        Date date2 = null;
        formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        try {
            date1 = (Date) formatter.parse(this.date + " " + this.time);
            date2 = (Date) formatter.parse(this.date + " " + this.time);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        catch(NullPointerException npe){
            System.out.println("Exception thrown "+npe.getMessage()+" date1 is "+date1+" date2 is "+date2);
        }

         return date1.compareTo(date2);

    }

    @Override
    public String toString(){       
        return this.date+" "+this.time;
    }

}

这是显示的输出:

2012-12-05 11:21:19
2012-12-05 11:20:19
2012-12-05 11:20:19
2012-12-04 10:20:19
2010-12-07 13:20:19
2012-12-05 11:20:19

此输出应为:

2010-12-07 13:20:19
2012-12-05 11:20:19
2012-12-05 11:20:19
2012-12-05 11:20:19
2012-12-05 11:21:19
2012-12-04 10:20:19

更新:当我将compareTo方法修改为:

public int compareTo(Object o) {


    DateFormat formatter;
    Date date1 = null;
    Date date2 = null;  
    DateObject other = (DateObject) o;

    formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    try {
        date1 = (Date) formatter.parse(this.date + " " + this.time);
        date2 = (Date) formatter.parse(other.date + " " + other.time);
    } catch (ParseException e) {
        e.printStackTrace();
    }
    catch(NullPointerException npe){
        System.out.println("Exception thrown "+npe.getMessage()+" date1 is "+date1+" date2 is "+date2);
    }

     return date1.compareTo(date2);

}

输出是:

2010-12-07 13:20:19
2012-12-04 10:20:19
2012-12-05 11:20:19
2012-12-05 11:20:19
2012-12-05 11:20:19
2012-12-05 11:21:19

由于2012-12-05应该在2012-12-04之前出现,这仍然是不正确的

Answer 1

您正在解析相同的日期两次:

date1 = (Date) formatter.parse(this.date + " " + this.time);
date2 = (Date) formatter.parse(this.date + " " + this.time);

应该是:

date1 = (Date) formatter.parse(this.date + " " + this.time);
DateObject other = (DateObject) o;
date2 = (Date) formatter.parse(other.date + " " + other.time);

你应该测试o是一个DateObject而不是null,然后再尝试使用它并使用它.

编辑

刚刚尝试使用更新的代码return date2.compareTo(date1);,我得到:

2012-12-05 11:21:19
2012-12-05 11:20:19
2012-12-05 11:20:19
2012-12-05 11:20:19
2012-12-04 10:20:19
2010-12-07 13:20:19

按降序排列(请注意,最后一个日期是2010年).