Variables & Data Types
Understand variables, primitive data types, declarations, assignment, and basic output.
Variables & Data Types is a free Java Academy lesson on CoddyKit. This is lesson 1 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Java Academy learning path, and your progress syncs across the web and the CoddyKit app. The Java Academy course includes 3 lessons in total.
What Are Variables
Variables store values your program can use and change. Think of a variable as a labeled box.
- Each variable has a type that defines what it can hold.
- Names should be short and meaningful (e.g.,
count,price). - Use one variable per distinct piece of information.
Types Overview
Primitive types:
int: whole numbers (e.g., 0, 7, -12)double: decimals (e.g., 3.5, -0.25)boolean:trueorfalsechar: one character
String holds text (it is a class, not a primitive): String name = "Ada";
Declare & Assign
Declare and assign:
int count = 3;- Type then name, optional initial value.
- Change later:
count = 10; - End each statement with a semicolon.
Literals
Literals are fixed values in code.
- Integers:
0,-5,42 - Doubles:
3.14,2.0 - Booleans:
true,false
Keep lines short for mobile. Break long expressions and add spaces around operators for readability.
Printing Values
Print values with System.out.println.
System.out.println("Count: " + count);When a String is involved, + concatenates text with values.
Variables Demo
Try it: Create Main.java, paste the code, run it, then change values and run again to see output updates.
public class Main {
public static void main(String[] args) {
int count = 3;
double price = 3.5;
boolean active = true;
String product = "Book";
System.out.println("Count: " + count);
System.out.println("Price: " + price);
System.out.println("Active: " + active);
System.out.println("Product: " + product);
count = 10;
System.out.println("Updated count: " + count);
}
}
Double Declaration
Quick check: Which line declares a double variable with the value 3.5 correctly?
Recap & Next
Recap: You learned variable purpose, primitive types, declaration/assignment, literals, and printing values.
Next: Work with user input and arithmetic expressions.
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Frequently Asked Questions
Is the “Variables & Data Types” lesson free?
Yes — the full text of “Variables & Data Types” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Java Academy course, upgrade to CoddyKit PRO. The Java Academy course includes 3 lessons in total.
What will I learn in “Variables & Data Types”?
Understand variables, primitive data types, declarations, assignment, and basic output. You practise Java Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Java Academy?
No prior experience is required. Java Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 1 of 3.
How long does the “Variables & Data Types” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Java Academy lesson?
Yes. Every Java Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Variables & Data Types
- Input & Expressions – Part 1
- Input & Expressions – Part 2