code: public ServiceFuture<List<VirtualNetworkUsageInner>> listUsageAsync(final String resourceGroupName, final String virtualNetworkName, final ListOperationCallback<VirtualNetworkUsageInner> serviceCallback) {
          return AzureServiceFuture.fromPageResponse(
              listUsageSinglePageAsync(resourceGroupName, virtualNetworkName),
              new Func1<String, Observable<ServiceResponse<Page<VirtualNetworkUsageInner>>>>() {
                  @Override
                  public Observable<ServiceResponse<Page<VirtualNetworkUsageInner>>> call(String nextPageLink) {
                      return listUsageNextSinglePageAsync(nextPageLink);
                  }
              },
              serviceCallback);
      }
docs: Lists usage stats.
  
  @param resourceGroupName The name of the resource group.
  @param virtualNetworkName The name of the virtual network.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object