Circular-queue.java

class CircularQueue {
    private int[] arr;
    private int front, rear, size, capacity;

    public CircularQueue(int capacity) {
        this.capacity = capacity;
        arr = new int[capacity];
        front = 0;
        rear = -1;
        size = 0;
    }

    public void enqueue(int data) {
        if (size == capacity) throw new RuntimeException("Queue is full");
        rear = (rear + 1) % capacity;
        arr[rear] = data;
        size++;
    }

    public int dequeue() {
        if (size == 0) throw new RuntimeException("Queue is empty");
        int val = arr[front];
        front = (front + 1) % capacity;
        size--;
        return val;
    }

    public int peek() {
        if (size == 0) throw new RuntimeException("Queue is empty");
        return arr[front];
    }

    public boolean isEmpty() {
        return size == 0;
    }

    public boolean isFull() {
        return size == capacity;
    }

    public static void main(String[] args) {
        CircularQueue cq = new CircularQueue(5);
        cq.enqueue(1);
        cq.enqueue(2);
        cq.enqueue(3);
        cq.enqueue(4);
        cq.enqueue(5);
        System.out.println(cq.dequeue());
        System.out.println(cq.peek());
        cq.enqueue(6);
        while (!cq.isEmpty()) System.out.print(cq.dequeue() + " ");
    }
}