public boolean isSet(_Fields field) {
      if (field == null) {
        throw new IllegalArgumentException();
      }

      switch (field) {
      case INTERFACE_NAME:
        return isSetInterfaceName();
      case IMPL_CLASS_NAME:
        return isSetImplClassName();
      case CLASS_NAMES:
        return isSetClassNames();
      case CLASSES:
        return isSetClasses();
      }
      throw new IllegalStateException();
    }