Suppose we want to extend the PositionalList ADT with a method, indexOf(p), that returns the current index of the element stored at position p. Write this method using only other methods of the PositionalList interface (not details of our LinkedPositionalList implementation). Write the necessary code to test the method. Hint: Count the steps while traversing the list until encountering position p.

interface Position { E getElement() throws IllegalStateException;

}

interface PositionalList extends Position{

int size();

boolean isEmpty();

Position first();

Position last();

Position before(Position p) throws IllegalArgumentException;

Position after(Position p) throws IllegalArgumentException;

Position addFirst(E e);

Position addLast(E e);

Position addBefore(Position p, E e) throws IllegalArgumentException;

Position addAfter(Positionp , E e) throws IllegalArgumentException;

E set(Position p, E e) throws IllegalArgumentException;

E remove(Position p) throws IllegalArgumentException; Iterator iterator();

Iterable> positions();

}