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🏗️ SOLID Principles
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🏗️ SOLID Principles
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Now · 1. 🎯 Learning Objectives
🏗️ SOLID Principles
1. 🎯 Learning Objectives
- Apply each SOLID principle with code examples
- Refactor code violating SOLID principles
- Explain why SOLID leads to maintainable code
2. 📖 Core Content
3.1 Single Responsibility (SRP)
"A class should have only one reason to change."
Violation: A Report class that generates data AND formats output AND saves to file. Fix: Separate into DataFetcher, ReportFormatter, ReportSaver.
3.2 Open-Closed (OCP)
"Open for extension, closed for modification."
Violation: Adding a new shape type requires modifying the area calculator. Fix: Use polymorphism — each shape implements getArea().
3.3 Liskov Substitution (LSP)
"Subtypes must be substitutable for their base types."
Violation: A Square extending Rectangle where setWidth() affects height. Fix: Don't inherit Square from Rectangle. Use a common Shape interface.
3.4 Interface Segregation (ISP)
"Clients should not be forced to depend on interfaces they don't use."
Violation: A Worker interface with work(), eat(), sleep() methods. Robot class forced to implement eat(). Fix: Split into Workable, Eatable, Sleepable interfaces.
3.5 Dependency Inversion (DIP)
"Depend on abstractions, not concretions."
Violation: A class directly instantiating its dependencies. Fix: Use dependency injection — pass dependencies through constructor.
4. 📝 Practice Questions
Q1: A class that handles database operations AND sends emails. Which SOLID principle is violated?Answer: Single Responsibility Principle (SRP). Database operations and email sending are separate concerns that should change independently. Split into DatabaseHandler and EmailService classes. Join Discord PreviousAgile & ScrumNextDesign Patterns