code: public static void runExample(
        AdManagerServices adManagerServices, AdManagerSession session, long customFieldId)
        throws RemoteException {
      // Get the CustomFieldService.
      CustomFieldServiceInterface customFieldService =
          adManagerServices.get(session, CustomFieldServiceInterface.class);
  
      // Create a statement to only select a single custom field by ID.
      StatementBuilder statementBuilder =
          new StatementBuilder()
              .where("id = :id")
              .orderBy("id ASC")
              .limit(1)
              .withBindVariableValue("id", customFieldId);
  
      // Get the custom field.
      CustomFieldPage page =
          customFieldService.getCustomFieldsByStatement(statementBuilder.toStatement());
  
      CustomField customField = Iterables.getOnlyElement(Arrays.asList(page.getResults()));
  
      // Update the custom field description.
      customField.setDescription("New custom field description");
  
      // Update the custom field on the server.
      CustomField[] customFields =
          customFieldService.updateCustomFields(new CustomField[] {customField});
  
      for (CustomField updatedCustomField : customFields) {
        System.out.printf(
            "Custom field with ID %d and name '%s' was updated.%n",
            updatedCustomField.getId(), updatedCustomField.getName());
      }
    }
docs: Runs the example.
  
  @param adManagerServices the services factory.
  @param session the session.
  @param customFieldId the ID of the custom field to update.
  @throws ApiException if the API request failed with one or more service errors.
  @throws RemoteException if the API request failed due to other errors.