code: public ServiceFuture<VirtualMachineExtensionInner> getAsync(String resourceGroupName, String vmName, String vmExtensionName, final ServiceCallback<VirtualMachineExtensionInner> serviceCallback) {
          return ServiceFuture.fromResponse(getWithServiceResponseAsync(resourceGroupName, vmName, vmExtensionName), serviceCallback);
      }
docs: The operation to get the extension.
  
  @param resourceGroupName The name of the resource group.
  @param vmName The name of the virtual machine containing the extension.
  @param vmExtensionName The name of the virtual machine extension.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object