Hey guys, welcome back to our Java course!
So far, we made our computer say Hello World. But today, we’ll teach it how to remember things.
Because honestly, a computer that only talks but forgets everything? That’s like having a friend who doesn’t even remember your name after 5 minutes. Pretty useless, right?
That’s why we have variables.
What are Variables?
Think of a variable as a box.
- You give the box a name.
- You decide what type of stuff can go in it.
- You put something inside.
Example:
int age = 16;
Here’s what’s happening:
int= type of data (whole numbers)age= name of the box16= value we are storing inside
Boom. Your computer now remembers your age.
Why Data Types?
Java is a very picky teacher. It wants you to be clear about what’s inside the box.
Is it text? Number? True/False? One letter?
That’s where data types come in.
Let’s go through the main ones with easy examples.
1. String – Text or Words
Used when you want to store names, sentences, or anything with letters.
String hero = "Iron Man";
String city = "New York";
Real life: When you type your name in a form → Java stores it in a String.
2. int – Whole Numbers
For numbers without decimal points.
int age = 16;
int followers = 5000;
Real life: Age, marks, number of people in a class.
3. double – Decimal Numbers
For numbers with decimal points (more accurate than float).
double height = 1.75;
double salary = 55000.75;
Real life: Money, height, temperature.
4. float – Decimal Numbers (less accurate than double)
Similar to double, but smaller and less precise.
float pi = 3.14f;
(Notice the f at the end — Java needs it to know it’s a float.)
5. boolean – True or False
Only two possible values: true or false.
boolean isStudent = true;
boolean isLoggedIn = false;
Real life: Is the light ON? Is the exam submitted? Yes or No.
6. char – One Single Character
For just one letter, symbol, or digit.
char grade = 'A';
char symbol = '$';
char number = '9';
(Use single quotes ' ').
7. byte – Tiny Whole Numbers
Range: -128 to 127.
byte age = 100;
Rarely used, but good if you need to save memory (like in small devices).
8. short – Small Whole Numbers
Range: -32,768 to 32,767.
short populationOfTown = 25000;
Bigger than byte, smaller than int.
9. long – Really Big Whole Numbers
When int is not enough. You must put L at the end.
long worldPopulation = 8000000000L;
Used for big numbers like populations or bank balances.
Quick Recap of Number Types
| Type | Range/Precision | Example Use |
|---|---|---|
| byte | tiny numbers | sensors, small devices |
| short | small numbers | small datasets |
| int | whole numbers (most used) | general counting |
| long | very large numbers | population, IDs |
| float | decimal (less accurate) | quick calculations |
| double | decimal (more accurate) | finance, science |
Real-Life Example: Passport Form
Here’s a simple Java program showing all of this in action:
public class PassportForm {
public static void main(String[] args) {
String name = "Tony Stark"; // text
int age = 45; // whole number
double height = 1.85; // decimal
char gender = 'M'; // one letter
boolean hasCriminalRecord = false; // true/false
long passportNumber = 123456789012L; // big number
System.out.println("Passport Application:");
System.out.println("Name: " + name);
System.out.println("Age: " + age);
System.out.println("Height: " + height);
System.out.println("Gender: " + gender);
System.out.println("Criminal Record: " + hasCriminalRecord);
System.out.println("Passport Number: " + passportNumber);
}
}
When you run it, it prints Tony Stark’s passport info like a real application form.
Iron Man Reference
Think of Jarvis in Iron Man.
Jarvis needs to remember Tony’s name, his suit’s battery percentage, his flight speed, his location…
All of those are variables with different data types.
Wrap Up
Today you learned:
- Variables = boxes to store info
- Data types = tell Java what kind of info is in the box
- 8 primitive data types + String
- Real-life uses in forms, apps, and games
Tomorrow, we’ll make the computer actually do math and logic with these variables. That’s when things get spicy!
Reference:
Learn more about Java Data Types on Oracle Docs
You can also check out:
- Learn Java Basics (Day 1) – Install JDK and Run Your First Program
- Learn Java Variables and Data Types (Day 2): Java for Beginners
- Beginner’s Guide to Web Development
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