Interview Q&A / Object-Oriented Programming

1. What are the SOLID principles? Explain each in simple words.

   SOLID is five design guidelines. Single responsibility (one reason to change), Open/closed (add features without editing working code), Liskov substitution (a child must work wherever its parent works), Interface segregation (small, focused interfaces) and Dependency inversion (depend on abstractions, not concrete classes).

   IntermediateIn-depth3 min read
2. What is the difference between an abstract class and an interface?

   An abstract class is a partially built parent that can hold state, constructors and shared code, and a class can extend only one. An interface is a contract of methods that a class promises to provide, and a class can implement many.

   IntermediateIn-depth2 min read
3. What is the difference between composition and inheritance, and when would you prefer composition?

   Inheritance is an "is-a" relationship where a class extends another and reuses its code. Composition is a "has-a" relationship where a class holds other objects and delegates work to them. Prefer composition by default because it keeps classes loosely coupled and lets you swap behaviour, and use inheritance only for a true, stable "is-a" relationship.

   IntermediateIn-depth3 min read