Chapter 8: Introduction to OOPs

What is Object Oriented Programming?

Object Oriented programming tries to map code instructions with real world making the code short and easier to understand.

Solving a problem by creating objects is one of the most popular approaches in programming. This is called Object Oriented Programming.

🔄 Code Reusability

Write once, use multiple times through inheritance

🛡️ Data Security

Encapsulation protects data from unauthorized access

🧩 Modularity

Break complex problems into smaller, manageable parts

What is DRY?

DRY stands for - Do not repeat yourself

It focuses on Code reusability

OOPs Terminology

1. Abstraction

Hiding internal details (show only essential info)

📱 You use this phone without bothering about how it was made.

2. Encapsulation

The act of putting various components together (in a capsule)

💻 Laptop is a single entity with wifi + Speaker + Storage in a single box!

In Java, encapsulation means that sensitive data can be hidden from users.

3. Inheritance

The act of deriving new things from existing things

🛺 Rickshaw ⇒ E-Rickshaw

📞 Phone ⇒ Smart Phone

Implements DRY!

4. Polymorphism

One entity many forms

📱 Smartphone → Phone

📱 Smartphone → Calculator

Classes and Objects

Class

A class is a blueprint for creating objects.

Contains info to create a valid object.

Object

An Object is an instantiation of a class. When a class is defined, a template (info) is defined. Memory is allocated only after object instantiation.

Class vs Object Analogy

📋 JEE Application Form

(Class - Blueprint)

↓

✍️ Filled by Student

(Object Creation Process)

↓

📄 Application for that Student

(Object - Instance)

How to Model a Problem in OOPs

We identify the following:

Noun → Class → Employee

Adjective → Attributes → name, age, salary

Verb → Methods → getSalary(), increment()

Example: Employee Management System

Component	Type	Examples
Employee	Class (Noun)	The main entity
name, age, salary	Attributes (Adjectives)	Properties of employee
getSalary(), increment()	Methods (Verbs)	Actions employee can perform

Remember: Any real world Object = Properties + Behaviour

Object in OOPs = Attributes + Methods

Writing a Custom Class

Basic Class Structure

Employee.java

public class Employee {
    int id;        // Attribute 1
    String name;   // Attribute 2
}

Class with Methods

EmployeeWithMethods.java

public class Employee {
    public int id;
    public String name;
    public int salary;
    
    public int getSalary() {
        return salary;
    }
    
    public void getDetails() {
        System.out.println("Employee ID: " + id);
        System.out.println("Employee Name: " + name);
        System.out.println("Employee Salary: " + salary);
    }
    
    public void setName(String newName) {
        name = newName;
    }
}

Using the Employee Class

EmployeeTest.java

public class EmployeeTest {
    public static void main(String[] args) {
        // Creating objects of Employee class
        Employee emp1 = new Employee();
        Employee emp2 = new Employee();
        
        // Setting attributes for emp1
        emp1.id = 101;
        emp1.name = "John Doe";
        emp1.salary = 50000;
        
        // Setting attributes for emp2
        emp2.id = 102;
        emp2.name = "Jane Smith";
        emp2.salary = 60000;
        
        // Using methods
        System.out.println("Employee 1 Details:");
        emp1.getDetails();
        
        System.out.println("\nEmployee 2 Details:");
        emp2.getDetails();
        
        // Modifying employee name
        emp1.setName("John Updated");
        System.out.println("\nAfter name update:");
        emp1.getDetails();
        
        // Getting salary
        System.out.println("\nEmployee 1 Salary: " + emp1.getSalary());
    }
}

Practice Set

Chapter 8 - Practice Set

1. Employee Class

Create a class Employee with following properties and methods:
• Salary (property) (int)
• getSalary (method returning int)
• name (property) (String)
• getName (method returning String)
• setName (method changing name)

2. CellPhone Class

Create a class CellPhone with methods to print "ringing...", "vibrating..." etc.

3. Square Class

Create a class Square with a method to initialize its side, calculating area, perimeter etc.

4. Rectangle Class

Create a class Rectangle & repeat problem 3.

5. Tommy Vercetti Class

Create a class Tommy Vercetti for Rockstar Games capable of hitting (print hitting...), running, firing etc.