Variables in Java Explained for Beginners

Introduction: What Are Variables in Java?

When writing a Java program, we often need to store data such as numbers, names, or results.
This stored data can change while the program is running.

To store such data, Java uses variables.

What Is a Variable?

A variable is a named memory location used to store data that can change during program execution.

In simple words:
A variable is like a container that holds information.

Why Variables Are Important in Java

Variables allow a program to:

  • Store user input

  • Perform calculations

  • Remember values

  • Produce meaningful output

Without variables, programs would be static and useless.

How to Declare a Variable in Java

In Java, a variable must be declared before it is used.

 

Syntax

dataType variableName;

Example

int age;

Here:

  • int → data type

  • age → variable name

How to Assign a Value to a Variable

You can assign a value using the assignment operator (=).

 
age = 25;

Or combine declaration and assignment:

 
int age = 25;

Using Variables in a Java Program

Example

class Demo {
    public static void main(String[] args) {
        int number = 10;
        System.out.println(number);
    }
}

Output:

 
10

Rules for Naming Variables in Java

Java follows specific rules for variable names:

  • Must start with a letter, _, or $
  • Can contain letters and digits
  • Cannot start with a number
  • Cannot use Java keywords
  • Case-sensitive

Valid Variable Names

  • age

  • totalMarks

  • _count

Invalid Variable Names

  • 1number

  • class

  • total marks

Types of Variables in Java

Java variables are mainly divided into three types.

 

1. Local Variables

Definition

Variables declared inside a method.

Characteristics

  • Created when method is called

  • Destroyed when method ends

  • Must be initialized before use

Example

void display() {
    int x = 10;
}

2. Instance Variables

Definition

Variables declared inside a class but outside methods.

Characteristics

  • Belong to an object

  • Each object gets its own copy

Example

class Student {
    int age;
}

3. Static Variables

Definition

Variables declared using the static keyword.

Characteristics

  • Shared among all objects

  • Only one copy exists

Example

class College {
    static String name = "ABC College";
}

Real-Life Analogy

Think of variables like labeled boxes:

  • The label → variable name

  • The box → memory location

  • The item inside → value

You can replace the item, but the box remains.

Frequently Asked Questions (FAQs)

Q1. Can a variable change its value in Java?

Yes. Variables can store different values during program execution.

 

Q2. Can I declare multiple variables at once?

Yes.

 
int a = 5, b = 10;

 

Q3. Is Java case-sensitive with variables?

Yes. Age and age are different variables.

 

Q4. Can variables store text?

Yes, using the String data type.

 

Q5. What happens if a variable is not initialized?

Local variables cause an error; instance variables get default values.