Queue_01.java

// Circular Queue Implementation using Array

public class Queue_01 {
    static class Queue {
        int arr[];
        int size;
        int front = -1;
        int rear = -1;

        Queue(int size) {
            this.size = size;
            arr = new int[size];
        }

        public boolean isEmpty() {
            return rear == -1 && front == -1;
        }

        public boolean isFull() {
            return (rear + 1) % size == front;
        }

        public void add(int data) {
            if (isFull()) {
                System.out.println("Overflow");
                return;
            }
            // if it's the 1st element
            if (front == -1) {
                front = 0;
            }

            rear = (rear + 1) % size;
            arr[rear] = data;
        }

        public int remove() {
            if (isEmpty()) {
                System.out.println("empty queue");
                return -1;
            }
            int res = arr[front];

            // if only 1 element is present
            if (front == rear) {
                front = rear = -1;
            } else {
                front = (front + 1) % size;
            }

            return res;
        }

        public int peek() {
            if (isEmpty()) {
                System.out.println("empty queue");
                return -1;
            }

            return arr[front];
        }
    }

    public static void main(String args[]) {
        Queue q = new Queue(5);
        q.add(1);
        q.add(2);
        q.add(3);
        q.add(4);
        q.add(5);
        System.out.println(q.remove());
        q.add(6);
        System.out.println(q.remove());
        q.add(7);

        while (!q.isEmpty()) {
            System.out.println(q.remove());
        }
    }
}