code: @Override
      public void readExternal(ObjectInput in)
          throws IOException {
  
          byte header = in.readByte();
  
          switch (header) {
              case BAHAI:
                  this.obj = this.readBahai(in);
                  break;
              default:
                  throw new InvalidObjectException("Unknown calendar type.");
          }
  
      }
docs: /*[deutsch]
  <p>Implementierungsmethode des Interface {@link Externalizable}. </p>
  
  @param   in      input stream
  @throws  IOException in any case of IO-failures