How to identify classes in Object-Oriented Programming from a given problem.

24 Dec 2023

Intermediate

Identifying entities in Object-Oriented Programming (OOP) involves recognizing the key components or objects that exist in a problem domain and determining how they interact with each other. Here are some steps to help you identify entities in OOP from a given problem:

Understand the Problem Domain:
- Before diving into code, thoroughly understand the problem you are trying to solve. Identify the key concepts, actions, and relationships involved.
Identify Nouns and Verbs:
- Identify nouns in the problem description as potential objects and verbs as potential methods or actions.
- Nouns often represent entities, and verbs represent the actions or behaviors those entities can perform.
Look for Real-World Objects:
- Identify real-world objects and their attributes. These real-world objects often translate directly into classes in OOP.
Define Classes:
- Create classes based on the identified objects. Each class should encapsulate the attributes (data) and behaviors (methods) associated with an entity.
Consider Relationships:
- Identify relationships between different entities. This includes one-to-one, one-to-many, and many-to-many relationships. Represent these relationships in your classes.
Encapsulation:
- Encapsulate related attributes and behaviors within a class. This means bundling the data (attributes) and methods that operate on the data together in a single unit.
Inheritance:
- Identify commonalities between classes and consider using inheritance to create a hierarchy of classes. Inheritance helps to reuse code and establish an "is-a" relationship.
Polymorphism:
- Identify situations where objects of different classes exhibit similar behaviors. Use polymorphism to allow objects of different classes to be treated as objects of a common base class.
Abstraction:
- Abstract away unnecessary details and focus on essential attributes and behaviors. Create abstract classes or interfaces to represent common features without specifying their implementation.
Modularity:
- Divide your problem into smaller, manageable modules or components. Each module should represent a coherent set of related functionalities.
Check for Redundancy:
- Avoid redundancy by ensuring that each class has a clear and distinct responsibility. Eliminate duplicate code and consolidate common functionalities.
Iterate and Refine:
- OOP design is an iterative process. Refine your design as you gain a deeper understanding of the problem or encounter new requirements.

Here's a simple example to illustrate these steps:

Problem: Modeling a Library System

1. Understand the Problem Domain:

Clarify: Specify the exact tasks involved in managing books, patrons, and transactions (e.g., searching, cataloging, borrowing, returning, reserving, tracking overdue items, handling fines).
Identify Actors: Determine who interacts with the system (e.g., librarians, patrons, system administrators).
Consider Data Storage: Decide on a suitable database or storage mechanism for persistent data.

2. Identify Nouns and Verbs (updated):

Nouns: Book, Patron, Transaction, Librarian, Library, Overdue Item, Fine
Verbs: Borrow, Return, Reserve, Search, Renew, Catalog, Issue, Pay, Track

3. Look for Real-World Objects (updated):

Book, Patron, Transaction, Librarian, Library

4. Define Classes:

Book class: title, author, ISBN, genre, publication date, availability status
Patron class: name, address, contact information, library card number, borrowing history
Librarian class: name, employee ID, access privileges
Transaction class: date, type (borrow, return, reserve), book, patron, due date, status (overdue, returned)
Library class: name, address, collection of books

5. Consider Relationships:

A Transaction involves a Book, a Patron, and possibly a Librarian.
A Book belongs to a Library.
A Librarian works at a Library.

6. Encapsulation:

Encapsulate attributes and behaviors within respective classes, protecting data integrity and promoting modularity.

7. Inheritance:

Consider potential subclasses for:
- Book: FictionBook, NonFictionBook, ReferenceBook
- Patron: AdultPatron, ChildPatron
- Librarian: HeadLibrarian, CirculationLibrarian

8. Polymorphism:

Explore opportunities for polymorphic behavior, such as different transaction types or book formatting.

9. Abstraction:

Identify common functionalities and abstract them into separate classes or interfaces for better maintainability.

10. Modularity:

Organize code into modules or packages for clarity and separation of concerns:
- BookManagement
- PatronManagement
- TransactionManagement
- LibrarianManagement
- LibraryManagement

11. Check for Redundancy:

Ensure each class has a clear and unique responsibility, avoiding unnecessary duplication.

12. Iterate and Refine:

Continuously review and refine the design based on feedback, changing requirements, and testing results.

Problem: Designing an Online Marketplace

1. Understand the Problem Domain:

Clarify: Specify the tasks involved in managing products, sellers, buyers, transactions (e.g., browsing, buying, selling, reviewing, tracking orders, handling payments).
Identify Actors: Determine who interacts with the system (e.g., sellers, buyers, administrators).
Consider Data Storage: Decide on a suitable database or storage mechanism for product listings, user profiles, and transaction history.

2. Identify Nouns and Verbs:

Nouns: Product, Seller, Buyer, Transaction, Administrator, Order
Verbs: Browse, Buy, Sell, Review, Track, Pay, Manage

3. Look for Real-World Objects:

Product, Seller, Buyer, Transaction, Administrator