Circular Queue ADT using arrays in Java!

Circular Queue :

Circular Queue is a linear data structure. It follows FIFO principle.

• In Circular Queue the last node is connected back to the first node to make a circle.
• Elements are added at the rear and deleted at front of the queue.
• Both the front and rear pointers point to the beginning of the array.
• Circular Queue is also called as Ring Buffer.
• Items can be inserted and deleted from a queue in O(1) time.

 Circular Queue can be created in three ways they are :

• Using arrays (In this post)
• Using single linked list
• Using double linked list

I'll be covering Circular Queue using Arrays and remaining two in next posts.

Program :

interface CQArrAdt{
    void insert();
    void delete();
    void display();
}
class CQArr1 implements CQArrAdt{
    int cq[],size,front,rear;
    Scanner s=new Scanner(System.in);
    public CQArr1()throws Exception{
        System.out.println("Enter the size of the Circular Queue :");
        size=s.nextInt();
        cq=new int[size];
        front=-1;rear=-1;
    }

    @Override
    public void insert() {
        if(((front==0) && (rear==cq.length-1))||(rear==front-1)){
            System.out.println("Circular Queue is full!!!");
        }
        else if(front==-1){front=0;rear=0;}
        else if(rear==cq.length-1)rear=0;//rotate/override cq
        else
            rear++;
        System.out.println("Enter the element into the circular queue :");
        int ele=s.nextInt();
        cq[rear]=ele;
        System.out.println("At this point rear= "+rear++);
    }

    @Override
    public void delete() {
        if(front==-1)
            System.out.println("CQ is underflow!!");
        else
        {
            System.out.println("Deleted item is :"+cq[front]);
            if(front==rear)//array contains only one element
            {
                front=rear=-1;
            }
            else if(front==cq.length-1){//rotate in the array!!!
                front=0;
            }
            else
                front--;
        }
    }

    @Override
    public void display() {
        if(front==-1){
            System.out.println("CQ is empty");
        }
        else if(front<=rear){
            for(int i=front;i<=rear;i++)
                System.out.print(" a"+cq[i]);
        }
        else{
            for(int i=front;i<cq.length;i++)
                System.out.print(" b"+cq[i]);
            for(int i=0;i<=rear;i++)
                System.out.print(" c"+cq[i]);
        }
    }
    
}
public class CQArr{
    public static void main(String args[]) throws Exception{
        System.out.println("Circular Queue ADT");
        Scanner s=new Scanner(System.in);
        CQArr1 c=new CQArr1();
        String ch="y";
        while(ch.equalsIgnoreCase("y")){
            System.out.println("Circular Queue operations\n1. Insert 2. Delete 3. Display 4. Exit\nEnter your choice :");
            int opt=s.nextInt();
            switch(opt){
                case 1:c.insert();break;
                case 2:c.delete();
                       break;
                case 3:c.display();break;
                case 4:System.exit(0);
                default :System.out.println("Invalid operation!!!");
            }
            System.out.println("Do you want to continue (y/N):");
            ch=s.next();
        }
    }
    
}