Java Variables – Declare, Initialize & Use Variables in Java

Introduction – What Are Variables in Java?

Every Java program revolves around data — and variables are how we store and manipulate that data. Think of a variable as a container with a label, used to hold different kinds of information like numbers, text, or boolean values.

Whether you’re calculating tax or storing user input, understanding Java variables is a fundamental step.

By the end of this guide, you’ll be able to:

• Declare and initialize variables
• Understand Java’s variable types and naming rules
• Use variables in expressions and output
• Follow best practices for clean, readable code

What Is a Variable in Java?

A variable in Java is a named memory location that stores a value.

Syntax:

type variableName = value;

Example:

int age = 25;

Explanation:

• int: data type (integer)
• age: variable name
• 25: value assigned to the variable

Types of Variables in Java

Java supports several types of variables, depending on where and how they are declared.

Tip: Always initialize local variables before using them.

Declaring and Initializing Variables

Declare First, Assign Later:

int score;
score = 100;

Declare and Assign Together:

String city = "Mumbai";

Multiple Variables of Same Type:

int x = 10, y = 20, z = 30;

Warning: Avoid using undeclared or uninitialized variables — it causes a compile-time error.

Variable Naming Rules

Allowed:

• Letters (a–z, A–Z)
• Digits (0–9)
• Underscore (_) and Dollar sign ($)

Not Allowed:

• Names starting with a digit
• Reserved keywords (class, int, etc.)

Examples:

Best Practice: Use camelCase for variables (firstName, totalAmount).

Example: Using Variables in Java

public class UserProfile {
    public static void main(String[] args) {
        String name = "Alice";
        int age = 30;
        double height = 5.7;

        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Height: " + height + " feet");
    }
}

Output:

Name: Alice
Age: 30
Height: 5.7 feet

Explanation:

• Different data types are used (String, int, double)
• All values are printed using System.out.println()

Java Variable Data Types (Quick Overview)

You’ll explore these in detail in the Java Data Types section.

Summary – Java Variables Essentials

Java variables are the foundation of storing and manipulating data. You’ve learned:

• How to declare and initialize variables
• Types of variables: local, instance, static
• Naming rules and best practices
• How to use variables in Java programs.

FAQs – Java Variables

What is a variable in Java?

A variable is a container that holds a value — like a label on a storage box in memory.

Can a Java variable name start with a number?

No. Variable names cannot begin with digits, but digits can be used after the first character.

What happens if I don’t initialize a variable?

• Local variables must be initialized before use — or you’ll get a compile error.
• Instance variables get default values (0, false, null, etc.).

What’s the difference between String and char?

• char: stores a single character ('A')
• String: stores a sequence of characters ("Apple")