sortfield does not has any effect when using with FieldComparator- Why?

i dont understand how sort by distance has been achieved using below
mentioned code.

Please explain me...how lucene handles sortfield if sortfield is ""?

   DistanceQueryBuilder queryBuilder = new
DistanceQueryBuilder(latitude, longitude, radius, "lat", "lon",
CartesianTierPlotter.DEFALT_FIELD_PREFIX, true);
   DistanceFieldComparatorSource distComp = new
DistanceFieldComparatorSource(queryBuilder.getDistanceFilter());
   Sort distSort = new Sort(new SortField("", distComp,false));


PS: i am using lucene 3.0.3

Raised the same here too.
http://stackoverflow.com/questions/22929423/how-lucene-handles-sortfield-with-comparator-if-sortfield-is


Kumaran R