Order a collection by date

[John Landon]

Hi,
What is the best way to order a Collection of ClassA by date. The date is stored in ClassA (like new ClassA().date)?

Thanks.

[John Landon]

There is a Collections.public static void sort(List list, Comparator c).
But what do I give it as c?

[Henry Wong]

Originally posted by John Landon:
There is a Collections.public static void sort(List list, Comparator c).
But what do I give it as c?

This is hardly an advanced questio. Perhaps this should be moved to beginners?

Anyway to answer your question. How about something like this?

public class DateCompare implements Comparator<ClassA> {
    public int compare(ClassA o1, ClassA o2) {
        Date first = o1.date;
        Date second = o1.date;
 
        return first.before(second) ? -1 :
               first.after(second) ? 1 : 0;
    }
}

Henry

[Paul Yule]

you need to create a class that implements the comparator...take a look at the comparator interface (2 methods). Or create an anonymous comparator that implements compare() on the spot:

 
sort(List list, new Comparator()
          {
                 public int compare( Object a, Object b ){//TODO}
          } );   

[Tom Johnson]

Give it a comparator....what else?!! You can use a named implementation or pass an anonymous implementation, as follows:

   
Collections.sort(collection, new Comparator() {
    public int compare(Object o1, Object o2) {
        // Do them compare by casting objects to ClassA and getting the date
        // of each and comparing them
        // Remember to handle nulls        
    }
});

Hope this helps
[ November 20, 2008: Message edited by: Tom Johnson ]

[John Landon]

Thanks. Just figured it out.