OOP Concepts Overview

OOP is usually explained through four main pillars:

1. Encapsulation
2. Inheritance
3. Polymorphism
4. Abstraction

You will study each deeply later. For now, learn the clean meaning of each one.

1. Encapsulation

Encapsulation means keeping data and related functions together inside a class, while controlling access to the data.

Example:

class BankAccount {
private:
    double balance;

public:
    void deposit(double amount);
    bool withdraw(double amount);
};

The balance is private. Outside code must use safe public functions.

One-Line Viva Answer

Encapsulation binds data and methods together and protects internal state from direct outside access.

2. Inheritance

Inheritance means creating a new class from an existing class.

It models an is-a relationship.

Example:

class Animal {};
class Dog : public Animal {};

A Dog is an Animal, so inheritance makes sense.

One-Line Viva Answer

Inheritance allows a derived class to reuse and extend a base class when there is a true is-a relationship.

3. Polymorphism

Polymorphism means "many forms."

In C++, it commonly means the same function call can behave differently depending on the actual object type.

Example idea:

animal->speak();

If animal points to a Dog, it may bark. If it points to a Cat, it may meow.

One-Line Viva Answer

Polymorphism allows one interface or function call to produce different behavior for different object types.

4. Abstraction

Abstraction means showing only essential details and hiding implementation complexity.

Example:

class PaymentProcessor {
public:
    virtual void pay(double amount) = 0;
};

The user knows they can call pay(). They do not need to know whether payment happens by card, mobile banking, or another method.

One-Line Viva Answer

Abstraction hides implementation details and exposes only the necessary interface.

How They Work Together

C++ Tools for These Pillars

Important Distinction

Encapsulation and abstraction are related, but not the same.

• Encapsulation protects internal state.
• Abstraction hides unnecessary details.

Example:

• A BankAccount hiding balance is encapsulation.
• A PaymentProcessor hiding card/mobile-bank implementation is abstraction.

Viva Answer

The four pillars of OOP are encapsulation, inheritance, polymorphism, and abstraction. Encapsulation protects state, inheritance models is-a relationships, polymorphism allows many forms of behavior through one interface, and abstraction hides implementation details behind a simple interface.

Quick Check

• Which pillar protects data?
• Which pillar uses is-a?
• Which pillar uses virtual functions often?
• Which pillar hides complex implementation details?