Today, we'll review key principles of Object-Oriented Design, including classes, objects, inheritance, and encapsulation. Remember, classes are blueprints of objects, while encapsulation groups data and methods.

Great question, Student_1! Encapsulation is all about restricting access to some of the object's components. It protects the object’s internal state from unauthorized access and modifications, which is crucial for maintaining data integrity.

Exactly! Instead, we use methods to interact with those properties, which helps enforce rules and keeps the object safe.

Certainly! Inheritance allows a new class to inherit attributes and methods from an existing class. For instance, if we have a class `Vehicle`, a class `Car` can inherit from it.

We can add methods specific to the `Car` class without affecting the `Vehicle` class, showcasing how inheritance allows flexibility in design. In summary, these principles work together to create modular and reusable code.

Now let's dive into our first example: the Library Management System. This system includes classes like `Book`, `Member`, and `Librarian`.

Excellent point, Student_3! The `Borrowing` class captures the transaction details when a member borrows a book, linking a `Book` to a `Member`.

The `Member` class can associate with multiple `Borrowing` instances, and a `Book` can be associated with multiple `Borrowing` records over time. This illustrates how real-world relationships can be modeled in our design.

Great observation, Student_4. We adhere to Low Coupling and High Cohesion, meaning each class has a specific responsibility and minimizes dependencies on others, simplifying design.

Let's move on to our second example: the Online Shopping Cart system.

We have `Customer`, `Product`, `ShoppingCart`, `Order`, and `PaymentGateway`. Each class plays a unique role.

The `Customer` can add `Product` entities to their `ShoppingCart`, and when they check out, an `Order` is created that references `OrderItems` linked to products.

In such cases, the `PaymentGateway` class handles any payment-related operations, and it can trigger alerts back to the `Order` class, guaranteeing a separation of duties.

Excellent question. By encapsulating payment logic within the `PaymentGateway`, we mitigate risks while adhering to security concerns in coding practices. Always remember, encapsulation keeps important components secure!

As we wrap up, let's briefly recap the core principles we've discussed today.

Absolutely! And we emphasized how these principles let us create flexible and maintainable software.

Low coupling allows you to change classes without affecting others, which is key to maintaining code in the long term.

Exactly right, Student_4! Together, these principles lead to better code structure and easier debugging. Remember – a well-designed software system is often a product of solid object-oriented practices.