Program to implement Circular Queue in JAVA

In this post we will learn about what are circular queues and how to implement circular queue in Java programming language. So, let’s start with definition of circular queue

What is Circular Queue in Java?

In  a standard queue data structure re-buffering problem occurs for each  dequeue operation. To solve this problem by joining the front and rear  ends of a queue to make the queue as a 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.
• Circular linked list fallow the First In First Out principle.
• Elements are added at the rear end and the elements are deleted at front end of the queue.
• Both the front and the rear pointers points to the beginning of the array.
• It is also called as “Ring buffer”.
• Items can inserted and deleted from a queue in O(1) time.

Program to implement Circular Queue in Java:

import java.io.*;
class CircularQ
{
	int Q[] = new int[100];
	int n, front, rear;
	static BufferedReader br = new BufferedReader(new
			InputStreamReader(System.in));
	public CircularQ(int nn)
	{
		n=nn;
		front = rear = 0;
	}
	public void add(int v)
	{
		if((rear+1) % n != front)
		{
			rear = (rear+1)%n;
			Q[rear] = v;
		}
		else
			System.out.println("Queue is full !");
	}
	public int del()
	{
		int v;
		if(front!=rear)
		{
			front = (front+1)%n;
			v = Q[front];
			return v;
		}
		else
			return -9999;
	}
	public void disp()
	{
		int i;
		if(front != rear)
		{
			i = (front +1) %n;
			while(i!=rear)
			{
				System.out.println(Q[i]);
				i = (i+1) % n;
			}
		}
		else
			System.out.println("Queue is empty !");
	}
	public static void main(String args[]) throws IOException
	{
		System.out.print("Enter the size of the queue : ");
		int size = Integer.parseInt(br.readLine());
		CircularQ call = new CircularQ(size);
		int choice;
		boolean exit = false;
		while(!exit)
		{
			System.out.print("\n1 : Add\n2 : Delete\n3 : Display\n4 : Exit\n\nYour Choice : ");
			choice = Integer.parseInt(br.readLine());
			switch(choice)
			{
				case 1 :
					System.out.print("\nEnter number to be added : ");
					int num = Integer.parseInt(br.readLine());
					call.add(num);
					break;
				case 2 :
					int popped = call.del();
					if(popped != -9999)
						System.out.println("\nDeleted : " +popped);
					else
						System.out.println("\nQueue is empty !");
					break;
				case 3 :
					call.disp();
					break;
				case 4 :
					exit = true;
					break;
				default :
					System.out.println("\nWrong Choice !");
					break;
			}
		}
	}
}

Sample Output:

$ javac CircularQ.java 
$ java CircularQ 
Enter the size of the queue : 5

1 : Add
2 : Delete
3 : Display
4 : Exit

Your Choice : 1

Enter number to be added : 31

1 : Add
2 : Delete
3 : Display
4 : Exit

Your Choice : 1

Enter number to be added : 28

1 : Add
2 : Delete
3 : Display
4 : Exit

Your Choice : 1

Enter number to be added : 9

1 : Add
2 : Delete
3 : Display
4 : Exit

Your Choice : 1

Enter number to be added : 56

1 : Add
2 : Delete
3 : Display
4 : Exit

Your Choice : 3
31
28
9

1 : Add
2 : Delete
3 : Display
4 : Exit