code: @Override
      protected PlainDate getDate0(int year) {
  
          int month = this.getMonthValue();
          int ref = GregorianMath.getDayOfWeek(year, month, this.dayOfMonth);
          PlainDate result = PlainDate.of(year, month, this.dayOfMonth);
  
          if (ref == this.dayOfWeek) {
              return result;
          }
  
          int delta = (ref - this.dayOfWeek);
          int sgn = -1;
  
          if (this.after) {
              delta = -delta;
              sgn = 1;
          }
  
          if (delta < 0) {
              delta += 7;
          }
  
          return result.plus(delta * sgn, DAYS);
  
      }
docs: ~ Methoden ----------------------------------------------------------