code: @Override
      public int prolepticYear(Era era, int yearOfEra) {
          if (era instanceof EthiopicEra == false) {
              throw new ClassCastException("Era must be EthiopicEra");
          }
          return (era == EthiopicEra.INCARNATION ? yearOfEra : 1 - yearOfEra);
      }
docs: -----------------------------------------------------------------------