Queue implementation using linkedlist in java

public class queue_ll {
    class Node{
        int data;
        Node next;
        Node(int data){
            this.data=data;
            this.next=null;
        }
    }
    Node front=null;
    Node rear=null;
    public void enqueue(int data){
        Node toadd=new Node(data);
        if (front==null){
            front=toadd;
            rear=toadd;
        }
        else{
            rear.next=toadd;
            rear=toadd;
        }
    }
    public void dequeue(){
        if (front==null){
            System.out.println("underflow");
        }
        else{
            front=front.next;
        }
    }
    public void display(){
        Node temp=front;
        while (temp!=null){
            System.out.println(temp.data);
            temp=temp.next;
        }
    }
    public static void main(String[] args) {
        queue_ll qll=new queue_ll();
        qll.enqueue(10);
        qll.enqueue(20);
        qll.enqueue(30);
        qll.enqueue(40);
        qll.display();
        System.out.println("********");
        qll.dequeue();
        qll.dequeue();
        qll.dequeue();
        qll.dequeue();
        qll.dequeue();
        qll.display();

    }
}