}

    @Override
    public E next() {
      return transferElement(nextElements, previousElements);
    }

    @Override
    public int nextIndex() {
      return previousElements.size();
    }

    @Override
    public E previous() {
      return transferElement(previousElements, nextElements);
    }

    @Override
    public int previousIndex() {

    }

    @Override
    public E next() {
      return transferElement(nextElements, previousElements);
    }

    @Override
    public int nextIndex() {
      return previousElements.size();
    }

    @Override
    public E previous() {
      return transferElement(previousElements, nextElements);
    }

    @Override
    public int previousIndex() {