Find the middle element of a singly-linked list in a single pass

public class Main{
    static class Node{
        int data;
        Node next;
        public Node(int data) {
            this.data = data;
            this.next = null;
        }
    }
    static class SinglyLinkedList{
        Node head;
        public SinglyLinkedList() {
            this.head = null;
        }
        public void addFront(int data){
            Node node = new Node(data);
            node.next = head;
            head = node;
        }
        public void printList(){
            Node temp = head;
            while(temp != null) {
                System.out.print(temp.data + " - ");
                temp = temp.next;
            }
            System.out.println("NULL");
        }
        public Node getMiddleElement(){
            if(head == null) {
                System.out.println("Empty list. Add elements to find the middle element");
                return null;
            }
            Node slowPtr = head;
            Node fastPtr = head;
            while(fastPtr != null && fastPtr.next != null){
                slowPtr = slowPtr.next;
                fastPtr = fastPtr.next.next;
            }
            return slowPtr;
        }
    }
    public static void main(String[] args) {
        SinglyLinkedList sll = new SinglyLinkedList();
        sll.addFront(5);
        sll.addFront(4);
        sll.addFront(3);
        sll.addFront(2);
        sll.addFront(1);
        sll.printList();
        System.out.println("Middle element for odd number of nodes in list is " + sll.getMiddleElement().data);
        System.out.println("----");
        sll = new SinglyLinkedList();
        sll.addFront(4);
        sll.addFront(7);
        sll.addFront(9);
        sll.addFront(5);
        sll.printList();
        System.out.println("Middle element for even number of nodes in list is " + sll.getMiddleElement().data);
    }
}