Lecture 42: Examples of Object-Oriented Design - Putting Principles into Practice
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Intro to Object-Oriented Design Principles
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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.
Could you explain what encapsulation really means?
Great question, Student_1! Encapsulation is all about restricting access to some of the object's components. It protects the objectβs internal state from unauthorized access and modifications, which is crucial for maintaining data integrity.
So, does that mean we can't directly change an object's properties?
Exactly! Instead, we use methods to interact with those properties, which helps enforce rules and keeps the object safe.
Can you give an example of inheritance?
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.
What if we wanted to add a specific behavior to just `Car` but not `Vehicle`?
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.
Library Management System Example
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Now let's dive into our first example: the Library Management System. This system includes classes like `Book`, `Member`, and `Librarian`.
What does the `Borrowing` class do?
Excellent point, Student_3! The `Borrowing` class captures the transaction details when a member borrows a book, linking a `Book` to a `Member`.
How do these classes relate to each other?
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.
That sounds like it could get complicated. What principles help us here?
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.
Online Shopping Cart Example
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Let's move on to our second example: the Online Shopping Cart system.
What are the key classes in this system?
We have `Customer`, `Product`, `ShoppingCart`, `Order`, and `PaymentGateway`. Each class plays a unique role.
How do they interact with each other?
The `Customer` can add `Product` entities to their `ShoppingCart`, and when they check out, an `Order` is created that references `OrderItems` linked to products.
What happens if a payment fails?
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.
How does this design maintain security?
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!
Design Principles Recap
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As we wrap up, let's briefly recap the core principles we've discussed today.
We covered classes, objects, inheritance, and encapsulation, right?
Absolutely! And we emphasized how these principles let us create flexible and maintainable software.
Why is low coupling particularly important?
Low coupling allows you to change classes without affecting others, which is key to maintaining code in the long term.
And high cohesion keeps our classes focused on one task?
Exactly right, Student_4! Together, these principles lead to better code structure and easier debugging. Remember β a well-designed software system is often a product of solid object-oriented practices.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
The section explores object-oriented design by showcasing examples like a Library Management System and an Online Shopping Cart. It emphasizes key concepts such as classes, inheritance, encapsulation, and relationships among the different components of the system.
Detailed
Detailed Summary
Overview
This section brings alive the concepts of Object-Oriented Design (OOD) using real-world applications that demonstrate the principles learned earlier. It illustrates how classes and objects are structured in practical scenarios and shows the use of important design aspects like inheritance, encapsulation, and relationships among different entities.
Key Concepts
- Classes and Objects: Classes act as blueprints from which objects are created. Each object instance contains data and behavioral methods.
- Abstraction and Encapsulation: Abstraction involves showing only essential details. Encapsulation ensures that the data and methods of an object are protected and controlled.
- Inheritance: This allows one class to inherit the properties and methods of another, promoting code reuse and a natural hierarchy.
- Polymorphism: This enables different objects to be treated as instances of the same class through a shared interface.
Examples
- Library Management System:
- Classes include
Book,Member,Librarian, andBorrowing. - Relationships define how members can borrow books and how the librarian manages the system.
- Online Shopping Cart:
- Classes include
Customer,Product,ShoppingCart,Order, andPaymentGateway. - Shows how customers interact with products, how orders are processed, and payment methods utilized.
Design Principles Illustrated
The section highlights good design practices such as high cohesion (each class focuses on one aspect) and low coupling (classes are independent). Proper encapsulation keeps data private, while the relationships show how to connect classes efficiently.
Key Concepts
-
Classes and Objects: Classes act as blueprints from which objects are created. Each object instance contains data and behavioral methods.
-
Abstraction and Encapsulation: Abstraction involves showing only essential details. Encapsulation ensures that the data and methods of an object are protected and controlled.
-
Inheritance: This allows one class to inherit the properties and methods of another, promoting code reuse and a natural hierarchy.
-
Polymorphism: This enables different objects to be treated as instances of the same class through a shared interface.
-
Examples
-
Library Management System:
-
Classes include
Book,Member,Librarian, andBorrowing. -
Relationships define how members can borrow books and how the librarian manages the system.
-
Online Shopping Cart:
-
Classes include
Customer,Product,ShoppingCart,Order, andPaymentGateway. -
Shows how customers interact with products, how orders are processed, and payment methods utilized.
-
Design Principles Illustrated
-
The section highlights good design practices such as high cohesion (each class focuses on one aspect) and low coupling (classes are independent). Proper encapsulation keeps data private, while the relationships show how to connect classes efficiently.
Examples & Applications
Library Management System:
Classes include Book, Member, Librarian, and Borrowing.
Relationships define how members can borrow books and how the librarian manages the system.
Online Shopping Cart:
Classes include Customer, Product, ShoppingCart, Order, and PaymentGateway.
Shows how customers interact with products, how orders are processed, and payment methods utilized.
Design Principles Illustrated
The section highlights good design practices such as high cohesion (each class focuses on one aspect) and low coupling (classes are independent). Proper encapsulation keeps data private, while the relationships show how to connect classes efficiently.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
Classes are blueprints that help create, Objects come alive, they operate.
Stories
Imagine building a car; first, you need a blueprint (class). You then assemble parts (objects) that run on a defined system (methods).
Memory Tools
CPOE - Class, Polymorphism, Objects, Encapsulation - remember the core OOD principles.
Acronyms
HCOL - High Cohesion, Low Coupling - the design principles to aim for.
Flash Cards
Glossary
- Class
A blueprint for creating objects, defining attributes and methods.
- Object
An instance of a class that can hold data and functions.
- Inheritance
A mechanism in OOP that allows a new class to inherit properties from an existing class.
- Encapsulation
The bundling of data and methods that operate on that data within one unit, restricting access to the inner workings.
- Polymorphism
A feature that allows methods to perform differently based on the object that is calling them.
- High Cohesion
The degree to which the elements of a module belong together.
- Low Coupling
A design principle that minimizes the interdependencies between modules.
Reference links
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