code: private long monthRange() {
          ValueRange startRange = chrono.range(MONTH_OF_YEAR);
          if (startRange.isFixed() && startRange.isIntValue()) {
              return startRange.getMaximum() - startRange.getMinimum() + 1;
          }
          return -1;
      }
docs: Calculates the range of months.
  
  @return the month range, -1 if not fixed range