if (isCancelled()) {
      builder.append("CANCELLED");
    } else if (isDone()) {
      addDoneString(builder);
    } else {
      addPendingString(builder); // delegates to addDoneString if future completes midway
    }
    return builder.append("]").toString();
  }

  /**
   * Provide a human-readable explanation of why this future has not yet completed.
   *

Niranjan Hasabnis, @Panmari, Pavel Bulanov, Philip Pries Henningsen, Philipp
Jund, @polonez, Prayag Verma, Rahul Kavi, Raphael Gontijo Lopes, @rasbt, Raven
Iqqe, Reid Pryzant, Richard Shin, Rizwan Asif, Russell Kaplan, Ryo Asakura,
RüDiger Busche, Saisai Shao, Sam Abrahams, @sanosay, Sean Papay, @seaotterman,
@selay01, Shaurya Sharma, Sriram Narayanamoorthy, Stefano Probst, @taknevski,