Circular Queue using Linked List in Java

import java.util.*;

class Main
{

  static class Node
  {
    int data;
    Node next;
  }

  static class Queue
  {
    Node front, rear;
  }

  static void enQueue (Queue q, int d)
  {
    Node tp = new Node ();
      tp.data = d;
    if (q.front == null)
      q.front = tp;
    else
        q.rear.next = tp;

      q.rear = tp;
      q.rear.next = q.front;
  }

  static int deQueue (Queue q)
  {
    if (q.front == null)
      {
	System.out.print ("empty queue");

      }

    int d;
    if (q.front == q.rear)
      {
	d = q.front.data;
	q.front = null;
	q.rear = null;
      }
    else
      {
	Node tp = q.front;
	d = tp.data;
	q.front = q.front.next;
	q.rear.next = q.front;
      }

    return d;
  }

  // Function displaying the elements
  static void displayQueue (Queue q)
  {
    Node tp = q.front;
    System.out.print ("Elements in Circular Queue are: ");
    while (tp.next != q.front)
      {
	System.out.print (tp.data + " ");
	tp = tp.next;
      }
    System.out.println (tp.data);
  }

  public static void main (String args[])
  {
    // Creating a queue
    Queue q = new Queue ();
    q.front = q.rear = null;

    // Inserting elements in Circular Queue
    enQueue (q, 20);
    enQueue (q, 40);
    enQueue (q, 60);

    // Display elements
    displayQueue (q);

    // Deleting elements
    System.out.println (deQueue (q));
    System.out.println (deQueue (q));
    System.out.println ("AFTER DELETING, ELEMENT LEFT  ");
    // Remaining elements in Circular Queue
    displayQueue (q);
    System.out.println ("AFTER INSERTING NEW VALUE ");
    enQueue (q, 80);
    displayQueue (q);
  }
}