The following incomplete Java program implements a Queue using a linked list. Complete the methods enqueue and dequeue.

// Java program for linked-list implementation of queue

// A linked list (LL) node to store a queue entry

class QNode {

int key;

QNode next;

// constructor to create a new linked list node

public QNode(int key)

{

this.key = key;

this.next = null;

}

}

// A class to represent a queue

// The queue, front stores the front node of LL and rear stores the

// last node of LL

class Queue {

QNode front, rear;

public Queue()

{

this.front = this.rear = null;

}

// Method to add an key to the queue.

void enqueue(int key)

{

// Create a new LL node

QNode temp = new QNode(key);

// If queue is empty, then new node is front and rear both

// TO COMPLETE

// Add the new node at the end of queue and change rear

// TO COMPLETE

}

// Method to remove an key from queue.

void dequeue()

{

// If queue is empty, return NULL.

if (this.front == null)

return;

// Store previous front and move front one node ahead

// TO COMPLETE

// If front becomes NULL, then change rear also as NULL

if (this.front == null)

this.rear = null;

}

}

// Driver class

public class Test {

public static void main(String[] args)

{

Queue q = new Queue();

q.enqueue(10);

q.enqueue(20);

q.dequeue();

q.dequeue();

q.enqueue(30);

q.enqueue(40);

q.enqueue(50);

q.dequeue();

System.out.println("Queue Front : " + q.front.key);

System.out.println("Queue Rear : " + q.rear.key);

}

}