Iterator class

private class LinkedListIterator implements Iterator<Data> {        // 1
    Node<Data> current = head;                                      // 2

    public boolean hasNext() {                                      // 3
        return current != null;                                     // 3
    }                                                               // 3

    public Data next() {                                            // 4
        Data data = current.data;                                   // 4
        current = current.next;                                     // 4
        return data;                                                // 4
    }
}