Question

因此，使用TreeMap，我能够按键（日期）对HashMap进行排序，但接下来要做的是，如果日期相同，那么我想按值（时间）排序。有人可以建议如何完成这项工作吗？

以下是按键正确排序的相关代码：

public void eventList(){

    int year = -1;
    if(MyCalendarTester.myCal.getMyCalHash().equals(null)){
        System.out.println("Your calendar is empty!");
    }
    else{
        System.out.println("Here are your events: ");
        SortedSet<GregorianCalendar> keys = new TreeSet<GregorianCalendar>(MyCalendarTester.myCal.getMyCalHash().keySet());

        for(GregorianCalendar key : keys){
            Event value = MyCalendarTester.myCal.getMyCalHash().get(key);
            if(value.endTime != null){
                if(key.get(Calendar.YEAR) == year){

                    System.out.println(MyCalendarTester.arrayOfDays[key.get(Calendar.DAY_OF_WEEK) - 1] + ", " + MyCalendarTester.arrayOfMonths[key.get(Calendar.MONTH) - 1] + " "
                            + key.get(Calendar.DATE) + " " + value.startTime.get(Calendar.HOUR_OF_DAY) + ":" + value.startTime.get(Calendar.MINUTE) + " - " + value.endTime.get(Calendar.HOUR_OF_DAY) 
                            + ":" + value.endTime.get(Calendar.MINUTE) + " " + value.eventName);

                }else{
                    System.out.println(key.get(Calendar.YEAR));
                    System.out.println(MyCalendarTester.arrayOfDays[key.get(Calendar.DAY_OF_WEEK) - 1] + ", " + MyCalendarTester.arrayOfMonths[key.get(Calendar.MONTH) - 1] + " "
                            + key.get(Calendar.DATE) + " " + value.startTime.get(Calendar.HOUR_OF_DAY) + ":" + value.startTime.get(Calendar.MINUTE) + " - " + value.endTime.get(Calendar.HOUR_OF_DAY) 
                            + ":" + value.endTime.get(Calendar.MINUTE) + " " + value.eventName );
                    year = key.get(Calendar.YEAR);
                }

            }else{
                if(key.get(Calendar.YEAR) == year){
                    System.out.println(MyCalendarTester.arrayOfDays[key.get(Calendar.DAY_OF_WEEK) - 1] + ", " + MyCalendarTester.arrayOfMonths[key.get(Calendar.MONTH) - 1] + " "
                            + key.get(Calendar.DATE) + " " + value.startTime.get(Calendar.HOUR_OF_DAY) + ":" + value.startTime.get(Calendar.MINUTE) + " " + value.eventName);

                }else{
                    System.out.println(key.get(Calendar.YEAR));
                    System.out.println(MyCalendarTester.arrayOfDays[key.get(Calendar.DAY_OF_WEEK) - 1] + ", " + MyCalendarTester.arrayOfMonths[key.get(Calendar.MONTH) - 1] + " "
                            + key.get(Calendar.DATE) + " " + value.startTime.get(Calendar.HOUR_OF_DAY) + ":" + value.startTime.get(Calendar.MINUTE)  + " " + value.eventName);
                    System.out.println();
                    year = key.get(Calendar.YEAR);
                }
            }

        }

    }

}

Answer 1

您需要创建一个嵌入键的两个组件的自定义Comparator

(date, time).

这样，您的数据会先按日期排序，然后按时间排序。

你可以通过将（日期，时间）组合成一个元组，然后在比较器中使用元组compareTo来实现这一点。

<强>更新
另一个选项是，如果您不希望更改键条目（这是btw map / reduce中的常见模式以进行二级排序..）：使您的值条目成为已排序的集合并迭代地比较集合条目。

比较可以通过

完成

merge()

mergesort的逻辑：两个列表需要单独降序排序。然后开始合并列表。这里的区别在于，只要找到任何差异，就会返回包含给定条目的列表

Answer 2

尝试使用此代码，根据日期时间

对所有Event对象进行排序

//* add a comparable to your event class
 public class Event implements Comparable
 {
  Calendar endTime = .....

  .....................


  public int compareTo(Object o)
  {
    Event  event = (Event)o;
    long  eventTime = event.endTime.getTimeInMillis();

    long time = endTime.getTimeInMillis();
    return (int)(time - eventTime);
  }
 }

//* loop over all of your event objects and add the correct date
for(GregorianCalendar key : keys)
{
   Event value = MyCalendarTester.myCal.getMyCalHash().get(key);
   value.endTime.set(Calendar.YEAR, key.get(Calendar.YEAR));
   value.endTime.set(Calendar.MONTH, key.get(Calendar.MONTH));
   value.endTime.set(Calendar.DAY_OF_MONTH, key.get(DAY_OF_MONTH));
}
//* get the array of all events and sort them
Event[] events = (Event[])MyCalendarTester.myCal.getMyCalHash().values().toArray(new Event[0]);
Arrays.sort(events);

按键对HashMap进行排序后，如果键匹配，如何按值排序

2 个答案: