Implement Queue using Linked List Java

PROGRAM TO IMPLEMENT QUEUE USING LINKED LIST

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

        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.

    void dequeue()

    {

        // If queue is empty, return NULL.

        if (this.front == null)

            return;

  

        // 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;

    }

}

  

// 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);

    }

}




OUTPUT:

Queue Front : 40
Queue Rear : 50

CREDITS: https://www.geeksforgeeks.org/queue-linked-list-implementation/