private class DLLIterator implements ListIterator<E> {
    private int index;
    private DoubleLinkedNode<E> node;
    private DoubleLinkedNode<E> lastNode;

    public DLLIterator() {
        index = 0;
        node = head;
        lastNode = null;
    }

    public DLLIterator(int index) throws IndexOutOfBoundsException {
        if (index < 0 || index >= size)
            throw new IndexOutOfBoundsException();

        this.index = index;
        node = head.getNext();
        for (int i=0; i < index; i++)
            node = node.getNext();
    }

    public boolean hasNext() {
        return size > 0;
    }

    public boolean hasPrevious() {
        return size > 0;
    }

    public E next() throws NoSuchElementException {
        if (size <= 0)
            throw new NoSuchElementException();

        node = nextFrom(node);
        lastNode = node;
        index = incIndex();

        return node.getValue();
    }

    public E previous() throws NoSuchElementException {
        if (size <= 0)
            throw new NoSuchElementException();

        if (node == head)
            node = head.getPrev();

        E value = node.getValue();
        lastNode = node;
        node = node.getPrev();
        index = decIndex();

        return value;
    }

    public int nextIndex() {
        if (size > 0)
            return incIndex();
        return -1;
    }

    public int previousIndex() {
        if (size > 0)
            return index;
        return -1;
    }

    public void remove() throws IllegalStateException {
        if (lastNode == null)
            throw new IllegalStateException();
        if (lastNode == node)
            node = node.getPrev();

        DoubleLinkedList.this.remove(lastNode);
        lastNode = null;
    }

    public void add(E element) {
        DoubleLinkedList.this.addBetween(element, node, node.getNext());
        next();
        lastNode = null;
    }

    public void set(E element) throws IllegalStateException {
        if (lastNode == null)
            throw new IllegalStateException();
        lastNode.setValue(element);
    }

    private int decIndex() {
        return (size + (index - 1)) % size;
    }

    private int incIndex() {
        return (index + 1) % size;
    }

    private DoubleLinkedNode<E> nextFrom(DoubleLinkedNode<E> node) {
        if (node == head.getPrev())
            return head.getNext();
        return node.getNext();
    }
}