code: public ServiceFuture<VirtualNetworkGatewayInner> createOrUpdateAsync(String resourceGroupName, String virtualNetworkGatewayName, VirtualNetworkGatewayInner parameters, final ServiceCallback<VirtualNetworkGatewayInner> serviceCallback) {
          return ServiceFuture.fromResponse(createOrUpdateWithServiceResponseAsync(resourceGroupName, virtualNetworkGatewayName, parameters), serviceCallback);
      }
docs: Creates or updates a virtual network gateway in the specified resource group.
  
  @param resourceGroupName The name of the resource group.
  @param virtualNetworkGatewayName The name of the virtual network gateway.
  @param parameters Parameters supplied to create or update virtual network gateway operation.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object