references: http://basicdatastructures.blogspot.in/2007/12/circular-queue-data-structure.html http://www.java2s.com/Tutorial/Java/0140__Collections/CircularQueue.htm http://www.flopsite.com/java-program-to-implement-circular-queue-using-array/

circularQueueInAarray.jav

package circularqueue;

/**
 *
 * @author Avinash
 */
public class CircularQueue {

    private int maxSize;
    private int[] cq;
    private int front = -1;
    private int rear = -1;
    private int count = 0;

    private void initialize(int maxSize) {
        this.maxSize = maxSize;
        cq = new int[this.maxSize];
        System.out.println("Circular Queue Initialized with the size of " + cq.length);
    }

    private void enqueue(int element) {
        if (front == (rear + 1) % this.maxSize) {
            System.out.println("Queue is already Full");
            System.out.println("error : Queue Overflows.");
        } else {
            rear = (rear + 1) % this.maxSize;
            cq[rear] = element;
            count++;
        }

        if (front == -1) {
            front = 0;
        }
    }

    private int dequeue() {
        int element = 0;
        if ((front == rear) && (rear == -1)) {
            System.out.println("Queue is already Empty");
            System.out.println("Error: Queue UnderFlows.");
        } else {
            element = cq[rear];
            count--;
            if (front == rear) {
                front = -1;
                rear = -1;
            } else {
                front = (front + 1) % this.maxSize;
            }
        }

        return element;
    }

    private void listQueue() {

        if (rear > front) {
            for (int i = front; i <= rear; i++) {
                System.out.println(cq[i]);
            }
        } else if (rear == front) {
            System.out.println(cq[rear]);
        } else if (rear < front) {
            for (int i = front; i < this.maxSize; i++) {
                System.out.println(cq[i]);
            }

            for (int i = 0; i <= rear; i++) {
                System.out.println(cq[i]);
            }
        }



    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        CircularQueue obj = new CircularQueue();
        obj.initialize(2);
        System.out.println("count : " + obj.count);
        System.out.println("front : " + obj.front + " : rear : " + obj.rear);
        System.out.println("");
        
        obj.enqueue(10);
        System.out.println("count : " + obj.count);
        System.out.println("front : " + obj.front + " : rear : " + obj.rear);
        System.out.println("");


        obj.enqueue(20);
        System.out.println("count : " + obj.count);
        System.out.println("front : " + obj.front + " : rear : " + obj.rear);
        System.out.println("");

//        obj.enqueue(30);
//        System.out.println("count : " + obj.count);
//        System.out.println("front : " + obj.front + " : rear : " + obj.rear);
//        System.out.println("");

        obj.listQueue();
        System.out.println("");

        obj.dequeue();
        System.out.println("count : " + obj.count);
        System.out.println("front : " + obj.front + " : rear : " + obj.rear);
        System.out.println("");

        obj.listQueue();
        System.out.println("");

        obj.enqueue(10);
        System.out.println("count : " + obj.count);
        System.out.println("front : " + obj.front + " : rear : " + obj.rear);
        System.out.println("");

        obj.listQueue();
        System.out.println("");

        obj.dequeue();
        System.out.println("count : " + obj.count);
        System.out.println("front : " + obj.front + " : rear : " + obj.rear);
        System.out.println("");

        obj.dequeue();
        System.out.println("count : " + obj.count);
        System.out.println("front : " + obj.front + " : rear : " + obj.rear);
        System.out.println("");

        obj.dequeue();
        System.out.println("count : " + obj.count);
        System.out.println("front : " + obj.front + " : rear : " + obj.rear);
        System.out.println("");


    }
}