code: static int compareCalendarDates(@NonNull Calendar first, @NonNull Calendar second) {
          final int firstYear = first.get(Calendar.YEAR);
          final int secondYear = second.get(Calendar.YEAR);
          final int firstDay = first.get(Calendar.DAY_OF_YEAR);
          final int secondDay = second.get(Calendar.DAY_OF_YEAR);
          if(firstYear == secondYear) {
              if(firstDay == secondDay)
                  return 0;
              else if(firstDay < secondDay)
                  return -1;
              else
                  return 1;
          }
          else if(firstYear < secondYear)
              return -1;
          else
              return 1;
      }
docs: Compares the two given Calendar objects, only counting the date, not time.
  @return -1 if first comes before second, 0 if both are the same day, 1 if second is before first.