* reasons).
 */
@GwtCompatible
abstract class AbstractIterator<T extends @Nullable Object> implements Iterator<T> {
  private State state = State.NOT_READY;

  protected AbstractIterator() {}

  private enum State {
    READY,
    NOT_READY,
    DONE,
    FAILED,
  }

  private @Nullable T next;

  protected abstract @Nullable T computeNext();

  @CanIgnoreReturnValue

 * reasons).
 */
@GwtCompatible
abstract class AbstractIterator<T extends @Nullable Object> implements Iterator<T> {
  private State state = State.NOT_READY;

  protected AbstractIterator() {}

  private enum State {
    READY,
    NOT_READY,
    DONE,
    FAILED,
  }

  private @Nullable T next;

  protected abstract @Nullable T computeNext();

  @CanIgnoreReturnValue

  private State state = State.NOT_READY;

  /** Constructor for use by subclasses. */
  protected AbstractIterator() {}

  private enum State {
    /** We have computed the next element and haven't returned it yet. */
    READY,

    /** We haven't yet computed or have already returned the element. */
    NOT_READY,

    /** We have reached the end of the data and are finished. */

  private State state = State.NOT_READY;

  /** Constructor for use by subclasses. */
  protected AbstractIterator() {}

  private enum State {
    /** We have computed the next element and haven't returned it yet. */
    READY,

    /** We haven't yet computed or have already returned the element. */
    NOT_READY,

    /** We have reached the end of the data and are finished. */