return nextIndex >= 0;
    }

    /**
     * Checks whether nextIndex is valid; if so setting nextItem. Stops iterator when either hits
     * putIndex or sees null item.
     */
    private void checkNext() {
      if (nextIndex == putIndex) {
        nextIndex = -1;
        nextItem = null;
      } else {
        nextItem = items[nextIndex];
        if (nextItem == null) nextIndex = -1;
      }
    }