public class SafeLinkedList {
    /* The head node of the list; never contains a real data item. */
    private Node head;
    /*
     * The size of the list; we use a variable so we don't have to iterate
     * through the list to get the size.  Needs to be updated in add/remove.
     */
    private int size;

    public SafeLinkedList() {
        head = new Node(null, null);
        size = 0;
    }

    /**
     * Adds an element to a certain index.  The index is similar to array
     * indexing, i.e., index 0 is the first element, etc.
     *
     * @param index The index to add the element at
     * @param elem  The element to add to the list
     */
    public void add(int index, Object elem) {
        if (index > size || index < 0) {
            throw new Error("Can't insert an item past the ends of the list");
        }
    }

    /**
     * Removes an object from the list.  The list is unaffected if the element
     * does not exist.
     *
     * @param elem The element to remove from the list
     */
    public void remove(Object elem) {
    }

    /**
     * Gets an object at a certain index.
     *
     * @param index The index to remove
     */
    public Object get(int index) {
        if (index > size || index < 0) {
            throw new Error("Can't retrieve an item past the ends of the list");
        }
    }

    /**
     * Appends an element to the list.  The same as calling add(list.size, elem)
     */
    public void append(Object elem) {
        add(size, elem);
    }

    /**
     * Returns the size of the list.
     */
    public int size() {
        return size;
    }

    /**
     * Removes all items from a list.
     */
    public void clear() {
        head.next = null;
        size = 0;
    }

    public String toString() {
        String ret = "";
        Node iter = head;
        for (int i = 0; i < size; i++, iter = iter.next) {
            ret += i + ": " + iter.next.element + "\n";
        }
        return ret;
    }

    class Node {
        public Object element;
        public Node< next;
        public Node(Object elem, Node next) {
            this.element = elem;
            this.next = next;
        }
    }
}