Stage 2 · Lesson 7 of 8
SOLID principles, at an introductory level
The are five guidelines for classes that are easy to change. Single responsibility: a class should have one reason to change. Open closed: you add new behaviour without editing code that already works and is tested.
Liskov substitution: a subclass keeps every promise its parent makes. Interface segregation: prefer small, focused interfaces over one huge one. Dependency inversion: depend on abstractions such as interfaces, not on specific classes.
Learn each with one small before and after example rather than a definition. They are tools for judgement, not laws. You will see them again when you read other people's code and study .
Common trapreciting the five names perfectly in an exam and then writing a 900-line class the next week.
A question to check yourself, an AI practice session and 1 cheat sheet entry come with the full roadmap. Unlock
Resources for this stage
Start with· follow one of these
- CoursePaidGrokking SOLID Design Principles
Design Gurus · Beginner · $50 one-time
Each SOLID principle with a broken example and its fix, at a beginner-friendly pace
- CourseFreeJava Programming MOOC
University of Helsinki · Beginner
Free, exercise-heavy course whose second half is a thorough, tested introduction to OOP