If you already know some coding and are tired of the DSA/Leetcode treadmill, the next logical step is to shift from solving puzzles to building systems. That means learning design patterns, SOLID principles, and architectural thinking — the things that actually show up in production code.
Here’s a practical roadmap, not theory:
1. Core Design Patterns (the real backbone of OOP)
Focus on why they exist, not just how they work.
- Creational: Singleton, Factory Method, Builder, Prototype → manage object creation (e.g. config loaders, factories for services).
- Structural: Adapter, Facade, Decorator, Composite → wrap APIs, extend behavior, simplify interfaces.
- Behavioral: Strategy, Observer, Command, Chain of Responsibility, State → modular logic, event systems, UI flows.
2. SOLID Principles (these shape all good code)
- S: Single Responsibility – one reason to change.
- O: Open/Closed – extend, don’t rewrite.
- L: Liskov Substitution – subclasses shouldn’t break parent contracts.
- I: Interface Segregation – smaller, focused interfaces.
- D: Dependency Inversion – depend on abstractions, not concrete implementations.
3. Modern Architectural Patterns
This is where real-world systems differ from toy problems:
- App level: MVC, MVVM, MVP → clean separation of logic and UI.
- System level: Hexagonal / Clean Architecture / CQRS → keep domain logic pure and isolated from frameworks.
- Concurrency: Actor Model, Event Sourcing, Reactor → for async, scalable systems.
- Integration: Pub/Sub, Saga, API Gateway, Message Bus → microservice reliability and communication.
4. Complementary skills that tie it all together
- Dependency Injection & IoC containers (Spring, NestJS, ASP.NET Core).
- Testing patterns (mocks, spies, test data builders).
- Domain-Driven Design for long-lived complex systems.
- Refactoring discipline — seriously, read Fowler’s Refactoring book.
5. How to actually learn it
- Refactor an existing project using one pattern at a time.
- Study real open-source repos (NestJS, ASP.NET, Django, etc.) and trace where patterns appear.
- Write small demo projects — Strategy for payments, Observer for events, etc.
- Don’t just read about patterns — apply them until they feel natural.
Once you get this down, you stop being “a coder” and start thinking like an engineer — someone who understands why this structure works, how it scales, and how it stays readable over time.