code: private static int getFirstCalendarWeekAsDayOfYear(int year) {
  
          Weekday wdNewYear =
              Weekday.valueOf(GregorianMath.getDayOfWeek(year, 1, 1));
          int dow = wdNewYear.getValue(Weekmodel.ISO);
  
          return (
              (dow <= 8 - Weekmodel.ISO.getMinimalDaysInFirstWeek())
              ? 2 - dow
              : 9 - dow
          );
  
      }
docs: Jahres auf einer day-of-year-Skala (kann auch <= 0 sein).