Java Programming Lesson 2 | Variables & Data Types Explained

LESSON - 2 VERIABLES AND DATA TYPES

Welcome to Lesson-2: Variables & Data Types 👨‍💻✨

📘 Lesson 2 — Variables & Data Types

✅ What is a Variable?

A variable is a container that stores data.

Example:
int age = 20; → age stores number 20

📌 Format:

dataType variableName = value;

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✅ Java Data Types

Java has 2 categories:

Category	Types	Examples
Primitive	8 types	int, float, char, boolean, long, double, byte, short
Non-Primitive	String, Array, Class	"Hello", {1,2,3}

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✅ Primitive Data Types (Most Used)

Type	Size	Example	Use
int	4 bytes	10	Whole numbers
float	4 bytes	5.5f	Decimal (less accurate)
double	8 bytes	8.99	Decimal (high accuracy)
char	2 bytes	'A'	Single character
boolean	1 bit	true/false	Conditions
long	8 bytes	99999999L	Big whole numbers

📌 Always remember:
float → add f
long → add L

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✅ Practical Example

public class VariablesExample {
    public static void main(String[] args) {

        int age = 21;
        float height = 5.7f;
        char grade = 'A';
        boolean isStudent = true;
        String name = "Jitu Hasan";

        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Height: " + height);
        System.out.println("Grade: " + grade);
        System.out.println("Is Student: " + isStudent);
    }
}

✅ Output:

Name: Jitu Hasan
Age: 21
Height: 5.7
Grade: A
Is Student: true

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✅ Naming Rules (Important Interview Question)

✔ Allowed: letters, numbers, _, $
✔ Must NOT start with a number
✔ Case-sensitive (age ≠ Age)
✔ No spaces

✅ Good:

studentName, totalMarks, age2

❌ Bad:

2amount, student name, class

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✅ Mini Exercise (Do it Now ✅)

Write a program using variables to print:

📌 Your Name
📌 Your Age
📌 Your Country
📌 Your Favorite Programming Language

Example Output:

My Name: _____
Age: _____
Country: _____
Favorite Language: _____

👉 Reply here with your code & output
I will check and improve it ✅

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🎯 Quick Quiz

1️⃣ Which is a non-primitive data type?
A) int
B) String
C) boolean

2️⃣ Which is correct?
A) float x = 5.5;
B) float x = 5.5f;

Reply like: 1 → ?, 2 → ?

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✅ Lesson-2 Completed!

Tell me when you're ready for:

➡ Lesson-3: Operators (Arithmetic, Logical, Relational)

Waiting for your answers + exercise 👇😊

▶ NEXT PART - Lesson-3: Operators