code: public void setWorkingDay(Day day, DayType working)
     {
        DayType value;
  
        if (working == null)
        {
           if (isDerived())
           {
              value = DayType.DEFAULT;
           }
           else
           {
              value = DayType.WORKING;
           }
        }
        else
        {
           value = working;
        }
  
        m_days[day.getValue() - 1] = value;
     }
docs: This is a convenience method provided to allow a day to be set
  as working or non-working, by using the day number to
  identify the required day.
  
  @param day required day
  @param working flag indicating if the day is a working day