code: private String getWorkingDayString(ProjectCalendar mpxjCalendar, Day day)
     {
        String result = null;
        net.sf.mpxj.DayType type = mpxjCalendar.getWorkingDay(day);
        if (type == null)
        {
           type = net.sf.mpxj.DayType.DEFAULT;
        }
  
        switch (type)
        {
           case WORKING:
           {
              result = "0";
              break;
           }
  
           case NON_WORKING:
           {
              result = "1";
              break;
           }
  
           case DEFAULT:
           {
              result = "2";
              break;
           }
        }
  
        return (result);
     }
docs: Returns a flag represented as a String, indicating if
  the supplied day is a working day.
  
  @param mpxjCalendar MPXJ ProjectCalendar instance
  @param day Day instance
  @return boolean flag as a string