@Override
public E pop() {
if (isEmpty()) throw new RuntimeException("Stack is already empty");
Node<E> node = ll.head();
E item = node.getKey();
ll.delete(node);
return item;
}
@Override
public String toString() {
return ll.toString();
}
@Override
public void push(E item) {
ll.insert(item);
}
@Override
public boolean isEmpty() {
return ll.head() == null;
}