OnlineShoppingBillingSystem.java

import java.util.*;

class Product {
    private int id;
    private String name;
    private double price;

    public Product(int id, String name, double price) {
        this.id = id;
        this.name = name;
        this.price = price;
    }

    public int getId() { return id; }
    public String getName() { return name; }
    public double getPrice() { return price; }
}

class CartItem {
    Product product;
    int quantity;

    public CartItem(Product product, int quantity) {
        this.product = product;
        this.quantity = quantity;
    }

    public double getTotal() {
        return product.getPrice() * quantity;
    }
}

class Customer {
    private String name;
    private ArrayList<CartItem> cart = new ArrayList<>();

    public Customer(String name) {
        this.name = name;
    }

    public void addToCart(Product product, int qty) {
        cart.add(new CartItem(product, qty));
    }

    public double getBill() {
        double total = 0;
        for (CartItem item : cart) {
            total += item.getTotal();
        }
        return total;
    }

    public void showBill() {
        System.out.println("\n========== BILL ==========");
        System.out.println("Customer: " + name);
        System.out.println("--------------------------");
        for (CartItem item : cart) {
            System.out.println(item.product.getName() + "  x" + item.quantity + " = ₹" + item.getTotal());
        }
        System.out.println("--------------------------");
        System.out.println("Grand Total: ₹" + getBill());
        System.out.println("==========================");
    }
}

public class OnlineShoppingBillingSystem {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        Product[] products = {
            new Product(1, "Laptop", 55000),
            new Product(2, "Mobile", 20000),
            new Product(3, "Headphones", 1500),
            new Product(4, "Smart Watch", 3000),
            new Product(5, "Pendrive", 500)
        };

        System.out.print("Enter customer name: ");
        String name = sc.nextLine();
        Customer customer = new Customer(name);

        while (true) {
            System.out.println("\n======= PRODUCT LIST =======");
            for (Product p : products) {
                System.out.println(p.getId() + ". " + p.getName() + " - ₹" + p.getPrice());
            }
            System.out.println("0. Checkout");
            System.out.print("\nEnter product ID to buy: ");
            int id = sc.nextInt();

            if (id == 0) break;

            Product selected = null;
            for (Product p : products) {
                if (p.getId() == id) {
                    selected = p;
                }
            }

            if (selected == null) {
                System.out.println("Invalid product ID!");
                continue;
            }

            System.out.print("Enter quantity: ");
            int qty = sc.nextInt();

            customer.addToCart(selected, qty);
            System.out.println("Added to cart successfully!");
        }

        customer.showBill();
        sc.close();
    }
}