Circular Queue in Java

import java.util.Scanner;

public class CircularQueue {

    private int front, rear, capacity;
    private int[] queue;

    public CircularQueue(int size) {
        capacity = size;
        queue = new int[capacity];
        front = -1;
        rear = -1;
    }

    // Check if queue is full
    public boolean isFull() {
        return (front == 0 && rear == capacity - 1) ||
               (front == (rear + 1) % capacity);
    }

    // Check if queue is empty
    public boolean isEmpty() {
        return front == -1;
    }

    // Enqueue operation
    public void enqueue(int value) {

        if (isFull()) {
            System.out.println("Queue is full. Cannot insert " + value);
            return;
        }

        if (front == -1) {   // first element
            front = 0;
        }

        rear = (rear + 1) % capacity;
        queue[rear] = value;
        System.out.println(value + " inserted");
    }

    // Dequeue operation
    public int dequeue() {

        if (isEmpty()) {
            System.out.println("Queue is empty (Underflow)");
            return -1;
        }

        int value = queue[front];

        // If this was the last element
        if (front == rear) {
            front = -1;
            rear = -1;
        } else {
            front = (front + 1) % capacity;
        }

        return value;
    }

    // View front element
    public int peek() {
        if (isEmpty()) {
            System.out.println("Queue is empty");
            return -1;
        }
        return queue[front];
    }

    // Display queue
    public void display() {

        if (isEmpty()) {
            System.out.println("Queue is empty");
            return;
        }

        System.out.print("CircularQueue: ");

        int i = front;
        while (true) {
            System.out.print(queue[i] + " ");
            if (i == rear) break;
            i = (i + 1) % capacity;
        }
        System.out.println();
    }

    // Main to test CircularQueue
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        System.out.print("Enter queue capacity: ");
        int cap = sc.nextInt();

        CircularQueue cq = new CircularQueue(cap);

        System.out.println("Choose operations:");
        System.out.println("1 = enqueue");
        System.out.println("2 = dequeue");
        System.out.println("3 = peek");
        System.out.println("4 = display");
        System.out.println("5 = exit");

        while (true) {
            System.out.print("\nEnter choice: ");
            int choice = sc.nextInt();

            switch (choice) {

                case 1:
                    System.out.print("Enter value: ");
                    int val = sc.nextInt();
                    cq.enqueue(val);
                    break;

                case 2:
                    int removed = cq.dequeue();
                    if (removed != -1) {
                        System.out.println("Removed: " + removed);
                    }
                    break;

                case 3:
                    System.out.println("Front: " + cq.peek());
                    break;

                case 4:
                    cq.display();
                    break;

                case 5:
                    System.out.println("Program terminated.");
                    sc.close();
                    return;

                default:
                    System.out.println("Invalid choice");
            }
        }
    }
}