What is Liskov Substitution Principle?

Short answer: The Liskov Substitution Principle (LSP) states that: Subtypes must be substitutable for their base types without altering the correctness of the program. In other words, if class S is a subclass of class T, then objects of type T should be replaceable with objects of type S without breaking the application. This ensures that inheritance models is-a relationships correctly.

Real-world example (ShopNest)

Patterns in ShopNest should solve a real pain (swappable payments, test seams)—not be added for decoration.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.