OOP Concepts for Interviews: Explained With Simple Examples
By the Codveri team ·
Encapsulation, inheritance, polymorphism and abstraction explained plainly, with the follow-up questions interviewers ask.
Why every interview asks about OOP
Object-oriented programming is how most large applications are organised. Interviewers use it to check whether you can structure code, not only write loops.
Encapsulation
Keep data and the methods that use it together, and hide the details. A bank account class exposes deposit and withdraw but keeps the balance private so no code can set it to a wrong value.
Follow-up: how is encapsulation different from abstraction? Encapsulation hides data; abstraction hides complexity behind a simple interface.
Inheritance
A child class reuses and extends a parent class. A Car is a Vehicle. Prefer inheritance for true is-a relationships and composition (has-a) when you only want to reuse behaviour.
Know that Java allows only single class inheritance but many interfaces, and that C++ allows multiple inheritance.
Polymorphism
The same call behaves differently depending on the object. Overloading is chosen at compile time by parameter types; overriding is chosen at run time by the actual object type. A shape.area() call works for circles and rectangles alike.
Abstraction and interfaces
An abstract class can hold shared code and unfinished methods; an interface describes only what a class can do. Use an interface when unrelated classes should share a capability.
Answer well
Use one real-world example per concept, say the benefit (reuse, safety or flexibility) and be ready to write five lines of code showing it.