code: public static JapaneseCalendar ofGregorian(
          Nengo nengo,
          int yearOfNengo,
          int month,
          int dayOfMonth
      ) {
  
          if (!nengo.isModern() || ((nengo == Nengo.MEIJI) && (yearOfNengo < 6))) {
              throw new IllegalArgumentException("Cannot create modern calendar with lunisolar calendar year.");
          }
  
          return JapaneseCalendar.of(nengo, yearOfNengo, EastAsianMonth.valueOf(month), dayOfMonth, Leniency.SMART);
  
      }
docs: /*[deutsch]
  <p>Erzeugt einen modernen japanischen Kalender f&uuml;r jedes Datum seit Meiji 6
  (gregorianische Kalenderregeln). </p>
  
  <p>Die gregorianische Bedingung au&szlig;er Acht lassend, &auml;quivalent zu
  {@code JapaneseCalendar.of(nengo, yearOfNengo, EastAsianMonth.valueOf(month), dayOfMonth, Leniency.SMART)}. </p>
  
  @param   nengo           Japanese era (Meiji or later)
  @param   yearOfNengo     year of nengo starting with number 1 (if Meiji then starting with 6)
  @param   month           gregorian month (1-12)
  @param   dayOfMonth      day of month {@code >= 1}
  @return  new instance of {@code JapaneseCalendar}
  @throws  IllegalArgumentException in case of any inconsistencies
  @see     #of(Nengo, int, EastAsianMonth, int, Leniency)