* Returns the first element.
     *
     * @return the first element
     */
    public E getFirst() {
        if (isEmpty()) {
            throw new NoSuchElementException();
        }
        return getFirstEntry().element;
    }

    /**
     * Returns the last element.
     *
     * @return the last element
     */
    public E getLast() {
        if (isEmpty()) {