code: public static String workDays(ProjectCalendar input)
     {
        StringBuilder result = new StringBuilder();
        DayType[] test = input.getDays(); // get the array from MPXJ ProjectCalendar
        for (DayType i : test)
        { // go through every day in the given array
           if (i == DayType.NON_WORKING)
           {
              result.append("N"); // only put N for non-working day of the week
           }
           else
           {
              result.append("Y"); // Assume WORKING day unless NON_WORKING
           }
        }
        return result.toString(); // According to USACE specs., exceptions will be specified in HOLI records
     }
docs: This method takes a calendar of MPXJ library type, then returns a String of the
  general working days USACE format.  For example, the regular 5-day work week is
  NYYYYYN
  
  If you get Fridays off work, then the String becomes NYYYYNN
  
  @param input ProjectCalendar instance
  @return work days string