} else if (isDone()) {
        addDoneString(builder);
      } else {
        builder.append("PENDING");
      }
    }
    return builder.append("]").toString();
  }

  /**
   * Provide a human-readable explanation of why this future has not yet completed.
   *
   * @return null if an explanation cannot be provided because the future is done.
   */
  @Nullable
  String pendingToString() {

        runStart = -1;
      }
    }
    if (bestRunLength >= 2) {
      Arrays.fill(hextets, bestRunStart, bestRunStart + bestRunLength, -1);
    }
  }

  /**
   * Convert a list of hextets into a human-readable IPv6 address.
   *
   * <p>In order for "::" compression to work, the input should contain negative sentinel values in
   * place of the elided zeroes.
   *

  @VisibleForTesting
  static WildcardType supertypeOf(Type lowerBound) {
    return new WildcardTypeImpl(new Type[] {lowerBound}, new Type[] {Object.class});
  }

  /**
   * Returns a human-readable string representation of {@code type}.
   *
   * <p>The format is subject to change.
   */
  static String toString(Type type) {
    return (type instanceof Class) ? ((Class<?>) type).getName() : type.toString();

   * response to a sender.
   *
   * @since 8.0
   */
  public static final byte ACK = 6;

  /**
   * Bell ('\a'): A character for use when there is a need to call for human attention. It may
   * control alarm or attention devices.
   *
   * @since 8.0
   */
  public static final byte BEL = 7;

  /**

 * <td>{@link #base16()}
 * <td>0-9 A-F
 * <td>2.00
 * <td>N/A
 * <td>Traditional hexadecimal. Defaults to upper case.
 * <tr>
 * <td>{@link #base32()}
 * <td>A-Z 2-7
 * <td>1.60
 * <td>=
 * <td>Human-readable; no possibility of mixing up 0/O or 1/I. Defaults to upper case.
 * <tr>
 * <td>{@link #base32Hex()}
 * <td>0-9 A-V
 * <td>1.60
 * <td>=

   * response to a sender.
   *
   * @since 8.0
   */
  public static final byte ACK = 6;

  /**
   * Bell ('\a'): A character for use when there is a need to call for human attention. It may
   * control alarm or attention devices.
   *
   * @since 8.0
   */
  public static final byte BEL = 7;

  /**