Implementation of Queues using two Stack in Java

import java.util.Stack;

class QueueUsingTwoStacks {

    private Stack stack1;
    private Stack stack2;

    // Constructor
    public QueueUsingTwoStacks() {
        stack1 = new Stack<>();
        stack2 = new Stack<>();
    }

    // Enqueue operation
    public void enqueue(int value) {
        stack1.push(value);
        System.out.println(value + " inserted");
    }

    // Dequeue operation
    public int dequeue() {

        // Underflow check
        if (stack1.isEmpty() && stack2.isEmpty()) {
            System.out.println("Queue is empty (Underflow)");
            return -1;
        }

        // Transfer elements if needed
        if (stack2.isEmpty()) {
            while (!stack1.isEmpty()) {
                stack2.push(stack1.pop());
            }
        }

        return stack2.pop();
    }

    // Peek operation
    public int peek() {

        if (stack1.isEmpty() && stack2.isEmpty()) {
            System.out.println("Queue is empty");
            return -1;
        }

        if (stack2.isEmpty()) {
            while (!stack1.isEmpty()) {
                stack2.push(stack1.pop());
            }
        }

        return stack2.peek();
    }

    // Check if queue is empty
    public boolean isEmpty() {
        return stack1.isEmpty() && stack2.isEmpty();
    }

    // Display queue elements
    public void display() {

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

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

        // Print stack2 (top to bottom)
        for (int i = stack2.size() - 1; i >= 0; i--) {
            System.out.print(stack2.get(i) + " ");
        }

        // Print stack1 (bottom to top)
        for (int i = 0; i < stack1.size(); i++) {
            System.out.print(stack1.get(i) + " ");
        }

        System.out.println();
    }

    // Main method
    public static void main(String[] args) {

        QueueUsingTwoStacks queue = new QueueUsingTwoStacks();

        // Enqueue
        queue.enqueue(10);
        queue.enqueue(20);
        queue.enqueue(30);

        // Display
        queue.display();

        // Peek
        System.out.println("Front element: " + queue.peek());

        // Dequeue
        System.out.println("Removed: " + queue.dequeue());
        System.out.println("Removed: " + queue.dequeue());

        // Display
        queue.display();

        // Enqueue again
        queue.enqueue(40);
        queue.enqueue(50);

        queue.display();

        // Dequeue remaining
        System.out.println("Removed: " + queue.dequeue());
        System.out.println("Removed: " + queue.dequeue());
        System.out.println("Removed: " + queue.dequeue());

        // Underflow test
        System.out.println("Removed: " + queue.dequeue());
    }
}