public interface LinkedListInterface<E extends Comparable<E>> {
    /**
     * The number of items in the linked list
     * 
     * @return the number of items in the linked list
     */
    int size();

    /**
     * Returns true iff the linked list has no elements
     * 
     * @return true iff the linked list has no elements
     */
    boolean isEmpty();

    /**
     * Get the first element in the linked list
     * 
     * @return the first element in the linked list or null is the list is empty
     */
    Comparable<E> first();

    /**
     * The last element in the linked list
     * 
     * @return the last elment or null is the list is empty
     */
    Comparable<E> last();

    /**
     * Add an element at the end of the list
     * 
     * @param c the element to be added
     */
    void addLast(Comparable<E> c);

    /**
     * Add a element at the front of the list
     * 
     * @param c the Element to be added
     */
    void addFirst(Comparable<E> c);

    /**
     * Remove the first element from the list
     * 
     * @return the first element, or null if the list is empty
     */
    Comparable<E> removeFirst();

    /**
     * Remove the last element from the list
     * 
     * @return the last element, or null if the list is empty
     */
    Comparable<E> removeLast();

    /**
     * Remove the specified element from the list
     * 
     * @param r the element to be removed
     * @return the removed element, or null is the element was not in the list
     */
    Comparable<E> remove(Comparable<E> r);

    /**
     * Find a element in the list by its iD
     * 
     * @param iD
     * @return the found element or null if a match could not be found
     */
    Comparable<E> find(Comparable<E> iD);
}