Object-Oriented Programming Basics

# CHAPTER 12

Object-Oriented Programming Basics #

1. Introduction #

2. Learning Objectives #

• Understand the OOP paradigm vs procedural programming.

• Learn the four pillars of OOP.

• Create classes and objects conceptually.

• Relate real-world entities to Java objects.

3. What is OOP? #

Procedural vs OOP:

4. The Four Pillars of OOP #

+------------------+------------------+
|  ENCAPSULATION   |  INHERITANCE     |
|  Wrapping data   |  Child classes   |
|  and methods     |  inherit from    |
|  together,       |  parent classes  |
|  hiding internals|                  |
+------------------+------------------+
|  POLYMORPHISM    |  ABSTRACTION     |
|  One interface,  |  Hiding complex  |
|  many forms      |  details, showing|
|  (method override)|  only essentials |
+------------------+------------------+

1. 1. Encapsulation: Bundling data + methods together and restricting direct access (using private and getters/setters).

1. 2. Inheritance: A class inheriting properties and methods from another class (extends).

1. 3. Polymorphism: The ability of an object to take many forms (method overloading and overriding).

1. 4. Abstraction: Hiding implementation details and showing only functionality (abstract classes and interfaces).

5. Real-World Analogy: The Car #

Class: Car (Blueprint)
├── Attributes: color, model, speed, fuelLevel
└── Methods: start(), accelerate(), brake(), refuel()

Objects (Instances):
├── myCar = new Car("Red", "Tesla Model 3")
├── yourCar = new Car("Blue", "Honda Civic")
└── taxiCar = new Car("Yellow", "Toyota Camry")

The Class is the blueprint. The Objects are the actual cars built from that blueprint.

6. Classes and Objects Overview #

// Class = Blueprint
public class Dog {
    String name;
    String breed;
    int age;
    
    void bark() {
        System.out.println(name + " says: Woof!");
    }
}

// Creating Objects
Dog dog1 = new Dog();
dog1.name = "Buddy";
dog1.breed = "Golden Retriever";
dog1.age = 3;
dog1.bark(); // "Buddy says: Woof!"

7. Benefits of OOP #

• Modularity: Code is organized into independent objects.

• Reusability: Classes can be reused across projects.

• Scalability: Easy to add new features without breaking existing code.

• Maintainability: Changes to one class don't affect others.

• Security: Data hiding through encapsulation.

8. Common Mistakes #

• Confusing classes with objects: A class is the blueprint; an object is the instance.

• Not understanding new: new Dog() allocates memory on the Heap.

• Overcomplicating: Not every program needs OOP. Simple scripts can be procedural.

9. MCQ Quiz with Answers #

10. Interview Questions #

• Q: Explain the four pillars of OOP with real-world examples.

• Q: Why is OOP preferred over procedural programming for large applications?

• Q: What is the relationship between a class and an object?

11. Summary #

12. Next Chapter Recommendation #