* instance method. In the unlikely event that you need to call this method, call {@link
   * InternalFutures#tryInternalFastPathGetFailure(InternalFutureFailureAccess)}.
   */
  protected abstract
      Throwable
      tryInternalFastPathGetFailure();

    return (Future<?>) settableFutureClass.getMethod("create").invoke(null);
  }

  private Throwable tryInternalFastPathGetFailure(Future<?> future) throws Exception {
    Method tryInternalFastPathGetFailureMethod =
        abstractFutureClass.getDeclaredMethod("tryInternalFastPathGetFailure");
    tryInternalFastPathGetFailureMethod.setAccessible(true);

    return (Future<?>) settableFutureClass.getMethod("create").invoke(null);
  }

  private Throwable tryInternalFastPathGetFailure(Future<?> future) throws Exception {
    Method tryInternalFastPathGetFailureMethod =
        abstractFutureClass.getDeclaredMethod("tryInternalFastPathGetFailure");
    tryInternalFastPathGetFailureMethod.setAccessible(true);

   *       return value of this method as its cause
   * </ul>
   */
  public static
      Throwable
      tryInternalFastPathGetFailure(InternalFutureFailureAccess future) {
    return future.tryInternalFastPathGetFailure();
  }

  private InternalFutures() {}

    future.set("261");
    assertThat(future.tryInternalFastPathGetFailure()).isNull();
  }

  public void testTrustedGetFailure_failed() {
    SettableFuture<String> future = SettableFuture.create();
    Throwable failure = new Throwable();
    future.setException(failure);
    assertThat(future.tryInternalFastPathGetFailure()).isEqualTo(failure);
  }

    future.set("261");
    assertThat(future.tryInternalFastPathGetFailure()).isNull();
  }

  public void testTrustedGetFailure_failed() {
    SettableFuture<String> future = SettableFuture.create();
    Throwable failure = new Throwable();
    future.setException(failure);
    assertThat(future.tryInternalFastPathGetFailure()).isEqualTo(failure);
  }

  final void addInitialException(Set<Throwable> seen) {
    checkNotNull(seen);
    if (!isCancelled()) {
      /*
       * requireNonNull is safe because:
       *
       * - This is a TrustedFuture, so tryInternalFastPathGetFailure will in fact return the failure
       *   cause if this Future has failed.
       *
       * - And this future *has* failed: This method is called only from handleException (through

      this.callback = callback;
    }

    @Override
    public void run() {
      if (future instanceof InternalFutureFailureAccess) {
        Throwable failure =
            InternalFutures.tryInternalFastPathGetFailure((InternalFutureFailureAccess) future);
        if (failure != null) {
          callback.onFailure(failure);
          return;
        }
      }
      V value;
      try {