// subclass is implemented with bugs similar to the subclass.
        pendingDescription = "Exception thrown from implementation: " + e.getClass();
      }
      // The future may complete during or before the call to getPendingToString, so we use null
      // as a signal that we should try checking if the future is done again.

  public String toString() {
    // TODO(cpovirk): Presize to something plausible?
    StringBuilder builder = new StringBuilder();
    if (getClass().getName().startsWith("com.google.common.util.concurrent.")) {
      builder.append(getClass().getSimpleName());
    } else {
      builder.append(getClass().getName());
    }
    builder.append('@').append(toHexString(identityHashCode(this))).append("[status=");
    if (isCancelled()) {