Implement Circular Queue using Array

 

package com.javainuse;

import java.util.Arrays;

public class CircularQueueImplementation {

    public static void main(String[] args) {

        CircularQueue<Integer> circularQueue = new CircularQueue(8);

        circularQueue.enqueue(15);
        circularQueue.enqueue(16);
        circularQueue.enqueue(17);
        circularQueue.enqueue(18);
        circularQueue.enqueue(19);
        circularQueue.enqueue(20);
        circularQueue.enqueue(21);
        circularQueue.enqueue(22);

        System.out.println("Full Circular Queue" + circularQueue);

        System.out.print("Dequeued following element from circular Queue ");
        System.out.println(circularQueue.dequeue() + " ");
        circularQueue.enqueue(23);
        System.out.println("After enqueueing circular queue with element having value 23");
        System.out.println(circularQueue);
    }

}

//implementation of Circular Queue using Generics
class CircularQueue<E> {

    private int currentSize; //Current Circular Queue Size
    private E[] circularQueueElements;
    private int maxSize; //Circular Queue maximum size

    private int rear;//rear position of Circular queue(new element enqueued at rear).
    private int front; //front position of Circular queue(element will be dequeued from front).      

    public CircularQueue(int maxSize) {
        this.maxSize = maxSize;
        circularQueueElements = (E[]) new Object[this.maxSize];
        currentSize = 0;
        front = 0;
        rear = 0;
    }

    /**
     * Enqueue elements to rear.
     */
    public void enqueue(E item) throws QueueFullException {
        if (isFull()) {
            throw new QueueFullException("Circular Queue is full. Element cannot be added");
        }
        else {
            circularQueueElements[rear] = item;
            rear = (rear + 1) % circularQueueElements.length;
            currentSize++;
        }
    }

    /**
     * Dequeue element from Front.
     */
    public E dequeue() throws QueueEmptyException {
        E deQueuedElement;
        if (isEmpty()) {
            throw new QueueEmptyException("Circular Queue is empty. Element cannot be retrieved");
        }
        else {
            deQueuedElement = circularQueueElements[front];
            circularQueueElements[front] = null;
            front = (front + 1) % circularQueueElements.length;
            currentSize--;
        }
        return deQueuedElement;
    }