Understand the idea

A variable associates a name and type with a value. Start with meaningful names such as lessonsCompleted. Assigning a new value changes what the variable holds; it does not change its declared type. Local variables must be assigned before you read them.

Explore the details

Java Variables

Variables are containers for storing data values.

In Java, there are different types of variables, for example:

• String – stores text, such as "Hello". String values are surrounded by double quotes
• int – stores integers (whole numbers), without decimals, such as 123 or -123
• float – stores floating point numbers, with decimals, such as 19.99 or -19.99
• char – stores single characters, such as 'a' or 'B'. Char values are surrounded by single quotes
• boolean – stores values with two states: true or false

Declaring (Creating) Variables

To create a variable in Java, you need to:

• Choose a type (like int or String)
• Give the variable a name (like x, age, or name)
• Optionally assign it a value using =

Here's the basic syntax:

Code anatomy / கோடின் விளக்கம்

For example, if you want to store some text, you can use a String:

To create a variable that should store a number, you can use int:

You can also declare a variable without assigning the value, and assign the value later:

Note that if you assign a new value to an existing variable, it will overwrite the previous value:

Final Variables

If you don't want others (or yourself) to overwrite existing values, use the final keyword (this will declare the variable as "final" or "constant", which means unchangeable and read-only):

Other Types

A demonstration of how to declare variables of other types:

// Declare then assign separately
int age;
age = 25;

// Declare and initialize together
String name = "Alice";
double salary = 45000.50;
boolean isActive = true;
char grade = 'A';

// Multiple vars of same type
int x = 10, y = 20, z = 30;

// var keyword (Java 10+) — type inferred
var city = "Chennai";   // String
var count = 100;         // int
System.out.println(city + " " + count);  // Chennai 100

A complete runnable example

This complete Main.java program focuses on the lesson idea. Reference fragments above may demonstrate individual statements; this example includes the imports, entry point, and supporting types it needs.

public class Main {
    public static void main(String[] args) throws Exception {
        String learner = "Kavi";
        int lessonsCompleted = 2;
        lessonsCompleted = lessonsCompleted + 1;
        System.out.println(learner + " completed " + lessonsCompleted + " lessons.");
    }
}

Kavi completed 3 lessons.

Change it. Run it. Understand it.

Load this lesson example into the editor. Change one value or statement, predict the result, then press RUN to execute Java.

Make it your own

Your learning checkpoint

• Explain the example without reading the output first.
• Make the change requested in the practice task.
• Describe why the result changed—or why compilation failed.

Ready to move on? Follow the next lesson in course order, or return to the curriculum to review a prerequisite.