private static int extractDataOfInterest(RentalZone zone, DataOfInterest what) { switch (what) { case STARTS: case INTERPOLATION: return zone.getRentalStarts(); case ENDS: return zone.getRentalEnds(); case SINKS: int sinks = zone.getRentalEnds() - zone.getRentalStarts(); if (sinks < 0) return -1; return sinks; case SOURCES: int source = zone.getRentalStarts() - zone.getRentalEnds(); if (source < 0) return -1; return source; default: return -1; } }