question: private void filterOutAboveOrBelowGround ( final Set < StendhalRPZone > zonesInRegion , final Boolean aboveGround ) { final Set < StendhalRPZone > removals = new HashSet < StendhalRPZone > ( ) ; for ( StendhalRPZone zone : zonesInRegion ) { if ( aboveGround . booleanValue ( ) ) { if ( zone . getLevel ( ) < 0 ) { removals . add ( zone ) ; } } else { if ( zone . getLevel ( ) >= 0 ) { removals . add ( zone ) ; } } } zonesInRegion . removeAll ( removals ) ; }
target:  Filter out zones above or below ground