public abstract class Customer {
    private ShoppingCart cart;
    private Order order;

    public ShoppingCart getShoppingCart();

    public bool addItemToCart(Item item);

    public bool removeItemFromCart(Item item);
}

public class Guest extends Customer {
    public bool registerAccount();
}

In the requirement it is mentioned that guest should not have access to place an order , but here guest extends the functionality of Customer which has Order in it , can you explain why do we have order in Customer class?