Software Engineering
Overview
Covers software engineering principles, SDLC methodologies, design patterns, clean code, and testing, based on the HKUST Software Engineering Specialization and HackerRank Certified Software Engineer.
SDLC Models
| Model | Description | Best For |
|---|---|---|
| Waterfall | Sequential phases, no going back | Fixed requirements |
| Agile | Iterative sprints, adaptive | Evolving requirements |
| Scrum | Agile framework with sprints, ceremonies | Product development |
| Kanban | Continuous flow, WIP limits | Operations/support |
| DevOps | Dev + Ops + CI/CD pipeline | Cloud-native teams |
Design Patterns
Creational
- Singleton, one instance globally (e.g., Logger, Config).
- Factory Method, delegate instantiation to subclasses.
- Builder, step-by-step construction of complex objects.
Structural
- Adapter, bridge incompatible interfaces.
- Decorator, add behaviour without modifying class.
- Proxy, control access to an object.
Behavioural
- Observer, subscribe/notify pattern (event systems).
- Strategy, swap algorithms at runtime.
- Command, encapsulate a request as an object.
SOLID Principles
| Letter | Principle |
|---|---|
| S | Single Responsibility, one reason to change |
| O | Open/Closed, open for extension, closed for modification |
| L | Liskov Substitution, subtypes replaceable for base type |
| I | Interface Segregation, prefer specific interfaces |
| D | Dependency Inversion, depend on abstractions |
Clean Code
- Meaningful names,
getUserByIdnotgetU. - Small functions, do one thing, do it well.
- No magic numbers, use named constants.
- DRY, Don't Repeat Yourself.
- YAGNI, You Aren't Gonna Need It (no speculative features).
- Comments explain why, not what (code should be self-explanatory).
Testing
| Type | Scope | Tool |
|---|---|---|
| Unit | Single function/class | JUnit, Vitest, pytest |
| Integration | Multiple components | Spring Boot Test, Testcontainers |
| E2E | Full user flow | Cypress, Playwright |
| Performance | Load and stress | JMeter, Gatling |
Test pyramid: Many unit tests → fewer integration tests → fewer E2E tests.
TDD (Test-Driven Development):
- Write a failing test (Red)
- Write minimum code to pass (Green)
- Refactor (Refactor)
Version Control & Code Review
- Small, focused commits with descriptive messages.
- Feature branches + Pull Requests for all changes.
- Code review checklist: correctness, readability, security, tests, performance.
- Semantic versioning:
MAJOR.MINOR.PATCH.
Cheat Sheet
SOLID: SRP | OCP | LSP | ISP | DIP
Patterns: Singleton | Factory | Builder | Observer | Strategy | Decorator
Testing: Unit → Integration → E2E (pyramid)
Clean code: Meaningful names | Small functions | DRY | YAGNI