* Returns a string representation for this CacheBuilder instance. The exact form of the returned
   * string is not specified.
   */
  @Override
  public String toString() {
    MoreObjects.ToStringHelper s = MoreObjects.toStringHelper(this);
    if (initialCapacity != UNSET_INT) {
      s.add("initialCapacity", initialCapacity);
    }
    if (concurrencyLevel != UNSET_INT) {
      s.add("concurrencyLevel", concurrencyLevel);

        callback.onFailure(e);
        return;
      }
      callback.onSuccess(value);
    }

    @Override
    public String toString() {
      return MoreObjects.toStringHelper(this).addValue(callback).toString();
    }
  }

  /**
   * Returns the result of the input {@code Future}, which must have already completed.
   *