code: public DateCalculator<LocalDate> setWorkingWeek(final WorkingWeek week) {
          if (week instanceof JodaWorkingWeek) {
              workingWeek = (JodaWorkingWeek) week;
              return this;
          }
          throw new IllegalArgumentException("Please give an instance of JodaWorkingWeek");
      }
docs: Set the working week.
  @param week the JodaWorkingWeek
  @throws IllegalArgumentException if the week is not a JodaWorkingWeek.