}

    @Override
    public <T> Future<T> submit(Callable<T> task) {
      throw new UnsupportedOperationException();
    }

    @Override
    public Future<?> submit(Runnable task) {
      throw new UnsupportedOperationException();
    }

    @Override
    public <T> Future<T> submit(Runnable task, T result) {
      throw new UnsupportedOperationException();
    }

  static <V extends @Nullable Object, X extends Exception> V getChecked(
      Future<V> future, Class<X> exceptionClass) throws X {
    return getChecked(bestGetCheckedTypeValidator(), future, exceptionClass);
  }

  /** Implementation of {@link Futures#getChecked(Future, Class)}. */
  @CanIgnoreReturnValue
  @VisibleForTesting
  @ParametricNullness
  static <V extends @Nullable Object, X extends Exception> V getChecked(

    checkNotNull(timeoutUnit);
    checkPositiveTimeout(timeoutDuration);

    Future<T> future = executor.submit(callable);

    try {
      return amInterruptible
          ? future.get(timeoutDuration, timeoutUnit)
          : getUninterruptibly(future, timeoutDuration, timeoutUnit);
    } catch (InterruptedException e) {
      future.cancel(true);
      throw e;
    } catch (ExecutionException e) {

        return new ExecutionListWrapper() {
          final AbstractFuture<?> future = new AbstractFuture<Object>() {};

          @Override
          public void add(Runnable runnable, Executor executor) {
            future.addListener(runnable, executor);
          }

          @Override
          public void execute() {
            future.set(null);
          }

        if (future.listenersField == expect) {
          future.listenersField = update;
          return true;
        }
        return false;
      }
    }

    @Override
    @Nullable Listener gasListeners(AbstractFutureState<?> future, Listener update) {
      synchronized (future) {
        Listener old = future.listenersField;
        if (old != update) {
          future.listenersField = update;

        if (future.listenersField == expect) {
          future.listenersField = update;
          return true;
        }
        return false;
      }
    }

    @Override
    @Nullable Listener gasListeners(AbstractFutureState<?> future, Listener update) {
      synchronized (future) {
        Listener old = future.listenersField;
        if (old != update) {
          future.listenersField = update;

    }
  }

  private enum Result {
    SUCCESS(immediateFuture(new Object())),
    FAILURE(immediateFailedFuture(new Exception()));

    final Future<Object> future;

    Result(Future<Object> result) {
      this.future = result;
    }
  }

  private enum ExceptionType {
    CHECKED(IOException.class),
    UNCHECKED(RuntimeException.class);

          }

          @Override
          public void onFailure(Throwable t) {
            failureCalls[0]++;
          }
        };
    addCallback(future, callback, directExecutor());
    future.set(result);
    assertEquals(result, future.get());
    assertThat(successCalls[0]).isEqualTo(1);
    assertThat(failureCalls[0]).isEqualTo(0);
  }

  public void testOnSuccessThrowsError() throws Exception {

 * result.
 *
 * @since 20.0
 */
@FunctionalInterface
@GwtCompatible
public interface AsyncCallable<V extends @Nullable Object> {
  /**
   * Computes a result {@code Future}. The output {@code Future} need not be {@linkplain
   * Future#isDone done}, making {@code AsyncCallable} suitable for asynchronous derivations.
   *
   * <p>Throwing an exception from this method is equivalent to returning a failing {@link

    SettableFuture<Integer> future = SettableFuture.create();
    assertTrue(future.set(42));
    // Later attempts to set the future should return false.
    assertFalse(future.set(23));
    assertFalse(future.setException(new Exception("bar")));
    assertFalse(future.setFuture(SettableFuture.<Integer>create()));
    // Check that the future has been set properly.
    assertTrue(future.isDone());
    assertFalse(future.isCancelled());