Queue.java

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

    public Queue(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) {
        Queue q = new Queue(5);
        q.enqueue(10);
        q.enqueue(20);
        q.enqueue(30);
        System.out.println(q.dequeue());
        System.out.println(q.peek());
        q.enqueue(40);
        q.enqueue(50);
        q.enqueue(60);
        System.out.println(q.isFull());
    }
}