public class MiddleNode {    public Node middle(Node headNode) {        if (headNode == null) {            System.out.println("this is no node in this list");            return null;        }        Node before = headNode;        Node behind = headNode;        while (before != null && before.next != null) {            before = before.next.next;            behind = behind.next;        }        return behind;    }}