code: private void writeObject(ObjectOutputStream stream) throws IOException{
          if (defaultCenturyStart == null) {
              // if defaultCenturyStart is not yet initialized,
              // calculate and set value before serialization.
              initializeDefaultCenturyStart(defaultCenturyBase);
          }
          initializeTimeZoneFormat(false);
          stream.defaultWriteObject();
          stream.writeInt(getContext(DisplayContext.Type.CAPITALIZATION).value());
      }
docs: Override writeObject.
  See http://docs.oracle.com/javase/6/docs/api/java/io/ObjectOutputStream.html