code: public ServiceFuture<VariableInner> updateAsync(String resourceGroupName, String automationAccountName, String variableName, VariableUpdateParameters parameters, final ServiceCallback<VariableInner> serviceCallback) {
          return ServiceFuture.fromResponse(updateWithServiceResponseAsync(resourceGroupName, automationAccountName, variableName, parameters), serviceCallback);
      }
docs: Update a variable.
  
  @param resourceGroupName Name of an Azure Resource group.
  @param automationAccountName The name of the automation account.
  @param variableName The variable name.
  @param parameters The parameters supplied to the update variable 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