@Override
      public Integer apply(Integer input) {
        return input + delta;
      }
    };
  }

  private static AsyncCallable<Integer> asyncAdd(
      final ListenableFuture<Integer> future, final int delta, final Executor executor) {
    return new AsyncCallable<Integer>() {
      @Override
      public ListenableFuture<Integer> call() throws Exception {

   * callable} or a callable that has begun to execute, but if the output future is cancelled before
   * {@link AsyncCallable#call()} is invoked, {@link AsyncCallable#call()} will not be invoked.
   */
  public <T extends @Nullable Object> ListenableFuture<T> submitAsync(
      AsyncCallable<T> callable, Executor executor) {
    checkNotNull(callable);
    checkNotNull(executor);

      @Override
      public Integer apply(Integer input) {
        return input + delta;
      }
    };
  }

  private static AsyncCallable<Integer> asyncAdd(
      final ListenableFuture<Integer> future, final int delta, final Executor executor) {
    return new AsyncCallable<Integer>() {
      @Override
      public ListenableFuture<Integer> call() throws Exception {

   * callable} or a callable that has begun to execute, but if the output future is cancelled before
   * {@link AsyncCallable#call()} is invoked, {@link AsyncCallable#call()} will not be invoked.
   */
  public <T extends @Nullable Object> ListenableFuture<T> submitAsync(
      AsyncCallable<T> callable, Executor executor) {
    checkNotNull(callable);
    checkNotNull(executor);