🧱 OOP

The four pillars, SOLID, and the design questions that follow them — the part of every interview that sounds easy until someone asks why.

Encapsulation

Bundling state with the code that's allowed to change it.

The is-a relationship — and the coupling that comes with it.

One interface, many implementations — resolved at compile time or run time.

Exposing what something does while hiding how it does it.

Five rules that mostly say: make change cheap.

Why 'favour composition' is the most repeated advice in OOP.

The choice that keeps changing as languages evolve.

The handful that actually come up, and what each one is for.

Reading these once won't hold

In the app these become flashcards on an expanding schedule, so you revisit each one just before you'd forget it.