}

  private boolean tryToComputeNext() {
    state = State.FAILED; // temporary pessimism
    next = computeNext();
    if (state != State.DONE) {
      state = State.READY;
      return true;
    }
    return false;
  }

  @Override
  @ParametricNullness
  public final T next() {
    if (!hasNext()) {
      throw new NoSuchElementException();
    }
    state = State.NOT_READY;

  }

  private boolean tryToComputeNext() {
    state = State.FAILED; // temporary pessimism
    next = computeNext();
    if (state != State.DONE) {
      state = State.READY;
      return true;
    }
    return false;
  }

  @Override
  @ParametricNullness
  public final T next() {
    if (!hasNext()) {
      throw new NoSuchElementException();
    }
    state = State.NOT_READY;

   * {@link #peek()} methods on this instance; if it does, an {@code IllegalStateException} will
   * result.
   *
   * @return the next element if there was one. If {@code endOfData} was called during execution,
   *     the return value will be ignored.
   * @throws RuntimeException if any unrecoverable error happens. This exception will propagate

   * {@link #peek()} methods on this instance; if it does, an {@code IllegalStateException} will
   * result.
   *
   * @return the next element if there was one. If {@code endOfData} was called during execution,
   *     the return value will be ignored.
   * @throws RuntimeException if any unrecoverable error happens. This exception will propagate