Question

Write a class that implements the Queue interface, as shown below. A queue is a data structure that accepts data and then returns it in the order in which it was received (first-in, first-out order). Items are added to the tail of the queue and removed from the head.

Your queue implementation must be accessible and usable from any package. However, any attempt to extend your class should produce a compile-time error.

*In java*

Answer 1

Please find my implementation.

Please let me know in case of any issue.

final public class 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;

       }

   }

  

   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

       if (this.rear == null)

       {

           this.front = this.rear = temp;

           return;

       }

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

       this.rear.next = temp;

       this.rear = temp;

   }

   // Method to remove an key from queue.

   QNode dequeue()

   {

       // If queue is empty, return NULL.

       if (this.front == null)

           return null;

       // Store previous front and move front one node ahead

       QNode temp = this.front;

       this.front = this.front.next;

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

       if (this.front == null)

           this.rear = null;

       return temp;

   }

}

###########

public class QueueTest

{

   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);

       System.out.println("Dequeued item is "+ q.dequeue().key);

   }

}