secondary sort using Comparator

[Tom Griffith]

Hello. if anybody has a minute, i can't seem to get this sort working. i am sorting vector elements and want to use the date as the primary sort and type as a secondary sort.

i thought i'd try something like this...


String type="widget";

String date_string="25-MAR-2005";

SimpleDateFormat dateFormat = new SimpleDateFormat("dd-MMM-yyyy");

Date date_object = dateFormat.parse(date_string);

long time_long=date_object.getTime();


String comparison_string=time_long+type;


then compare the string of time_long+type in the comparator to sort the elements by date and type.

However, my problem comes when the time_long value hits 999 then goes to 1000 say, creating an extra numerical digit. the comparator, since i'm comparing long_time+type strings, will sort the comparison strings with the highest number of time_long digits first, then sort, in order, the lesser number of time_long digits.

For instance, early Sept, 2001 does this...Sept 5 is 999658800000 seconds since 1970...12 digits...while Sept 9 is 1000004400000 seconds from 1970...13 digits....so the sort places Sept 9 entries first, sorts the 13 digit vector elements properly from Sept 9 to the latest date...then goes back to the earliest 12 digit elements and sorts those up through Sept 5. I hope this is understandable...again, i bother to convert these longs to text strings so i can incorporate the Type as the secondary sort. Thank you for reading this.

[Paul Clapham]

Then don't mash everything into a string. Basically your comparator should look something like this:

int result = firstDate.compareTo(secondDate);
if (result == 0) {
  result = firstString.compareTo(secondString);
}
return result;

In other words:

1. Compare the two dates. If they are different then return that information. If they are the same then compare the two Strings and return that information instead.

[Rob Spoor]

And you can do this as many times as you need. Simply return the first non-0 difference. You'll only return 0 if all fields you check are equal in comparison.