code: public void attachHoursToDay(ProjectCalendarHours hours)
     {
        if (hours.getParentCalendar() != this)
        {
           throw new IllegalArgumentException();
        }
        m_hours[hours.getDay().getValue() - 1] = hours;
     }
docs: Attaches a pre-existing set of hours to the correct
  day within the calendar.
  
  @param hours calendar hours instance