The SOLID design principles provide a set of guidelines for writing maintainable, flexible, and extensible code. Let’s explore a real-world example to see how these principles can be applied in practice.
Imagine a software system for managing a library. Initially, the system has a single `Book` class responsible for handling all book-related functionality, such as storing book details, rendering book information on the UI, and persisting data to a database. Over time, as the system grows, this single class becomes bloated and difficult to maintain.
By applying the SOLID principles, we can refactor the system into a more modular and maintainable design:
1. Single Responsibility Principle: We split the `Book` class into separate classes, each with a single responsibility. The `Book` class now only handles storing book details, while separate classes like `BookRenderer` and `BookRepository` handle UI rendering and database persistence, respectively.
2. Open-Closed Principle: We create abstractions for the rendering and persistence logic using interfaces like `IBookRenderer` and `IBookRepository`. This allows the system to be open for extension (e.g., adding new rendering formats) but closed for modification of existing code.
3. Liskov Substitution Principle: We ensure that any subclasses of `Book`, such as `Ebook` or `Audiobook`, can be used interchangeably with the base `Book` class without breaking the system’s behavior.
4. Interface Segregation Principle: Instead of having a single large interface for all book-related operations, we create smaller, focused interfaces like `IBookDetails`, `IBookRenderer`, and `IBookPersistence`. This allows clients to depend only on the interfaces they need.
5. Dependency Inversion Principle: High-level modules (e.g., the main application logic) depend on abstractions (interfaces) rather than concrete implementations. This enables loose coupling and easier testability.
By adhering to the SOLID principles, the library management system becomes more modular, maintainable, and adaptable to future changes. Each component has a clear responsibility, making the codebase easier to understand and modify.
Author: John Rowan
I am a Senior Android Engineer and I love everything to do with computers. My specialty is Android programming but I actually love to code in any language specifically learning new things.Share this:
