Stage 2 · Lesson 6 of 8
Composition over inheritance
means building an object out of other objects that it holds and hands work to. A Car has an Engine; it is not a kind of engine. With composition you can swap behaviour while the program runs.
A game character, for example, can be given a different way of moving without a new for every combination. Composition keeps classes small and loosely linked, so changes cost less. "Favour composition over inheritance" is a guideline, not a ban: inheritance still fits true "is a" relationships.
This idea sits under several you will meet next, such as Strategy and Decorator.
Common trapa class hierarchy that multiplies, such as FlyingSwimmingDuck, because every new combination of features needs its own subclass.
A question to check yourself, an AI practice session and 2 cheat sheet entries 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