📘 OOP Review (Object-Oriented Programming)
🔹 1. What is OOP?
Object-Oriented Programming (OOP) is a programming approach where software is designed using objects, which combine data (attributes) and behavior (methods).
👉 Simple idea:
Programs are built by modeling real-world entities like Car, Student, BankAccount as objects.
🔹 2. Basic Building Blocks
🔸 2.1 Class
- A blueprint/template for creating objects
- Defines attributes and methods
Example:
Class: Student
Attributes: name, rollNo
Methods: study(), attendClass()
🔸 2.2 Object
- An instance of a class
- Represents a real entity
Example:
Student s1 = new Student();
🔸 2.3 Attributes & Methods
| Component |
Meaning |
| Attributes |
Data (variables) |
| Methods |
Functions (behavior) |
🔹 3. Four Pillars of OOP ⭐
🔸 3.1 Abstraction
- Show only important details
- Hide complex implementation
Example:
Using a mobile phone without knowing internal circuits
🔸 3.2 Encapsulation
- Wrapping data + methods together
- Restrict direct access to data
Example:
private balance;
public deposit();
🔸 3.3 Inheritance
- One class inherits properties of another
Example:
Animal → Dog
Benefit: Code reuse
🔸 3.4 Polymorphism
- One function behaves differently in different situations
Types:
- Method Overloading
- Method Overriding
🔹 4. Important Concepts
🔸 4.1 Message Passing
Objects communicate by calling each other's methods
🔸 4.2 Dynamic Binding
Method call is resolved at runtime
🔸 4.3 Association Relationships
| Type |
Meaning |
| Association |
General relation |
| Aggregation |
Weak ownership |
| Composition |
Strong ownership |
🔸 4.4 Constructor
- Special method used to initialize objects
🔸 4.5 Destructor (in some languages)
- Used to free memory/resources
🔹 5. Advantages of OOP
- Reusability
- Security (data hiding)
- Easy maintenance
- Real-world modeling
- Scalability
🔹 6. Simple Example
👉 Bank System
Class:
BankAccount
- balance
+ deposit()
+ withdraw()
Object:
acc1.deposit(1000)
🔹 7. OOP vs Procedural Programming
| Feature |
OOP |
Procedural |
| Focus |
Objects |
Functions |
| Data Security |
High |
Low |
| Reusability |
High |
Limited |
🔹 8. Key Rules to Remember
- Use classes to model real-world objects
- Keep data private (encapsulation)
- Use inheritance for reuse
- Apply polymorphism for flexibility
🔹 9. Likely Exam Questions
- What is OOP? Explain with example.
- Define class and object.
- Explain the four pillars of OOP.
- What is encapsulation and why is it important?
- Describe inheritance with types.
- What is polymorphism? Give examples.
- Differentiate OOP and procedural programming.
- What is dynamic binding?
- Explain aggregation vs composition.
- What are advantages of OOP?
🔹 10. Quick Revision Summary 🧠
-
OOP = Objects + Classes
-
Class → Blueprint
-
Object → Instance
-
4 Pillars:
- Abstraction
- Encapsulation
- Inheritance
- Polymorphism
👉 Shortcut Trick:
"AEIP" (Abstraction, Encapsulation, Inheritance, Polymorphism)