Linear Queue ADT using Single Linked List

Program :

package adsa;
import java.util.Scanner;
/**
 *
 * @author sudeep
 */
interface LQSll{
    void insert();
    void delete();
    void display();
}
class QNode{
    int data;
    QNode link;
}
class QueueSll extends QNode implements LQSll{
    QNode front,rear;
    Scanner s=new Scanner(System.in);
    public QueueSll(){
        front=rear=null;
    }
    public void insert(){
        System.out.println("Insert the element into the linear Queue :");
        int ele=s.nextInt();
        QNode p=new QNode();
        p.data=ele;
        p.link=null;
        if(front==null)
            front=p;
        else rear.link=p;
        rear=p;
    }
    public void delete()
    {
        //QNode temp;
        if(front==null)
            System.out.println("Linear Queue is empty");
        else
        {
            //temp=front;
            System.out.println("Deleted item :"+front.data);
            front=front.link;
        }
    }
    public void display(){
        QNode temp;
        if(front==null)
            System.out.println("Linear Queue is empty");
        else{
            System.out.println("Queue elements are:");
            for(temp=front;temp!=null;temp=temp.link)
                System.out.println("-->"+temp.data);
        }
    }
    
    public static void main(String[] args){
        System.out.println("Single Linked List Linear Queue ADT");
        Scanner s=new Scanner(System.in);
        QueueSll q=new QueueSll();
        String ch="y";
        while(ch.equalsIgnoreCase("y")){
            System.out.println("\n Linear Queue ooperations :");
            System.out.println("1. Insert 2.Delete 3. Display 4.Exit");
            System.out.println("Enter the option :");
            int opt=s.nextInt();
            switch(opt){
                case 1:q.insert();break;
                case 2:q.delete();break;
                case 3:q.display();break;
                case 4:System.exit(0);
                default:System.out.println("Invalid option ");
            }
            System.out.println("Do you want to continue");
            ch=s.next();
        }
    }
}