code: protected int compareByTime(CalendarDate date) {
  
          long d1 = this.getDaysSinceEpochUTC();
          long d2 = date.getDaysSinceEpochUTC();
  
          return ((d1 < d2) ? -1 : ((d1 == d2) ? 0 : 1));
  
      }
docs: <p>Definiert eine rein zeitliche Ordnung. </p>
  
  <p>Diese Implementierung wertet die zeitliche Position auf dem
  gemeinsamen Zeitstrahl aus, also die Epochentage. </p>
  
  @param   date    another date to be compared with
  @return  negative, zero or positive integer if this instance is earlier,
  simultaneous or later than given date