OOP real world example

Question

I have a simple shopping cart model with products that are based on productID, productName, Price, and Stock columns from a database. I then have a productID,ProductName,Price item class that represents the item a customer decides to order. The itemOrder class then refers to the item via productID, ProductName, Price, and quantity via a getPrice method (). The itemOrders are then stored in a Cart class, which contains methods for adding and deleting itemOrders.

Where do OOP principles come into play in any of these classes or in a conventional shopping cart system?

public class Product
{
    public int productID { get; set; }
    public string productName { get; set; }
    ...
 }
}

public class Item : Product
{

}

public class ItemOrder : Item
{
    public int itemQuantity { get; set; }
    public double getPrice(int quantity, double price)
    {
        return price = price * quantity;
    }

}
public class Cart
{

}

Answer 1

This is what I believe.

OOP does not require inheritance. You have OOP if each of your classes effectively performs a single task while concealing any internal specifics from the outside world, providing a constant interface that clients cannot exploit to destroy the objects.

There's this principle called Liskov Substitution Principle and you should use inheritance if the relationship between two classes meets this principle.

Each of the three terms- item, product, and order are distinct and cannot be used in place of the others. All three classes must exist, but they must not share any common ancestors. Instead of using inheritance, Carts, Items, and Orders can refer to Products and to one another through references or confinement.