Question

Not quite sure how I should attack this. I need to create a Comparator for a class called Record. These records have a time I will use, but if the time is the same, I need to order them depending on their type. Say for example we have the following Record subtypes:

• AaRecord
• BbRecord
• CcRecord
• DdRecord

Now, given a collection with a number of these, I need to order them so that for example all CcRecord come before BbRecord followed by AaRecord and finally DdRecord. What is a good and clean way of doing this?

Just to be clear, I can’t use the names of the types to do this, as they could be anything. It’s going to be used to process a list of records in the correct order.

public class RecordComparator implements Comparator<Record>
{
   @Override
   public int compare(Record x, Record y)
   {
      // First compare times
      int result = x.getTime().compareTo(y.getTime());
      if(result != 0)
         return result;

      // Then somehow compare types...

   }
}

Answer 1

You could define a Map<Class, Integer> containing the sort orders for all the types, and then do this:

@Override
public int compare(Record x, Record y)
{
   // First compare times
   int result = x.getTime().compareTo(y.getTime());
   if(result != 0)
      return result;

   // sortOrders is your map
   return sortOrders.get(x.getClass()).compareTo(sortOrders.get(y.getClass()));
}

Or something like that.

Keep in mind that it doesn’t have to be integers.