Singly linked list java program

public class SinglyLinkedList {    
    //Represent a node of the singly linked list    
    class Node{    
        int data;    
        Node next;    
            
        public Node(int data) {    
            this.data = data;    
            this.next = null;    
        }    
    }    
     
    //Represent the head and tail of the singly linked list    
    public Node head = null;    
    public Node tail = null;    
        
    //addNode() will add a new node to the list    
    public void addNode(int data) {    
        //Create a new node    
        Node newNode = new Node(data);    
            
        //Checks if the list is empty    
        if(head == null) {    
            //If list is empty, both head and tail will point to new node    
            head = newNode;    
            tail = newNode;    
        }    
        else {    
            //newNode will be added after tail such that tail's next will point to newNode    
            tail.next = newNode;    
            //newNode will become new tail of the list    
            tail = newNode;    
        }    
    }    
        
    //display() will display all the nodes present in the list    
    public void display() {    
        //Node current will point to head    
        Node current = head;    
            
        if(head == null) {    
            System.out.println("List is empty");    
            return;    
        }    
        System.out.println("Nodes of singly linked list: ");    
        while(current != null) {    
            //Prints each node by incrementing pointer    
            System.out.print(current.data + " ");    
            current = current.next;    
        }    
        System.out.println();    
    }    
        
    public static void main(String[] args) {    
            
        SinglyLinkedList sList = new SinglyLinkedList();    
            
        //Add nodes to the list    
        sList.addNode(1);    
        sList.addNode(2);    
        sList.addNode(3);    
        sList.addNode(4);   
            
        //Displays the nodes present in the list    
        sList.display();    
    }    
}