}
  }

  public void testDefaultBehaviorOfPeek() {
    /*
     * This sample AbstractIterator returns 0 on the first call, 1 on the
     * second, then signals that it's reached the end of the data
     */
    AbstractIterator<Integer> iter =
        new AbstractIterator<Integer>() {
          private int rep;

          @Override
          public @Nullable Integer computeNext() {

    }
  }

  public void testDefaultBehaviorOfPeek() {
    /*
     * This sample AbstractIterator returns 0 on the first call, 1 on the
     * second, then signals that it's reached the end of the data
     */
    AbstractIterator<Integer> iter =
        new AbstractIterator<Integer>() {
          private int rep;

          @Override
          public @Nullable Integer computeNext() {

 *   <li>{@link ObjectArrays}
 *   <li>{@link Queues}
 *   <li>{@link Sets}
 *   <li>{@link Streams}
 *   <li>{@link Tables}
 * </ul>
 *
 * <h2>Abstract implementations</h2>
 *
 * <ul>
 *   <li>{@link AbstractIterator}
 *   <li>{@link AbstractSequentialIterator}
 *   <li>{@link UnmodifiableIterator}
 *   <li>{@link UnmodifiableListIterator}
 * </ul>
 *
 * <h2>Forwarding collections</h2>
 *

    PostOrderNode(T root, Iterator<T> childIterator) {
      this.root = checkNotNull(root);
      this.childIterator = checkNotNull(childIterator);
    }
  }

  private final class PostOrderIterator extends AbstractIterator<T> {
    private final ArrayDeque<PostOrderNode<T>> stack;

    PostOrderIterator(T root) {
      this.stack = new ArrayDeque<>();
      stack.addLast(expand(root));
    }

    @Override