code: public ServiceFuture<NamespaceResourceInner> createOrUpdateAsync(String resourceGroupName, String namespaceName, NamespaceCreateOrUpdateParameters parameters, final ServiceCallback<NamespaceResourceInner> serviceCallback) {
          return ServiceFuture.fromResponse(createOrUpdateWithServiceResponseAsync(resourceGroupName, namespaceName, parameters), serviceCallback);
      }
docs: Creates/Updates a service namespace. Once created, this namespace's resource manifest is immutable. This operation is idempotent.
  
  @param resourceGroupName The name of the resource group.
  @param namespaceName The namespace name.
  @param parameters Parameters supplied to create a Namespace Resource.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object