How to Declare Variables in Java: Syntax and Examples

In Java, you declare a variable by specifying its type followed by a name. For example, int age; declares an integer variable named age. You can also assign a value during declaration like int age = 25;.

Syntax

To declare a variable in Java, you write the type of the variable first, then the variable name, and optionally assign a value using the = sign. Every declaration ends with a semicolon ;.

• Type: The kind of data the variable will hold (e.g., int, double, String).
• Name: The identifier you choose to refer to the variable.
• Value (optional): The initial data assigned to the variable.

java

type variableName;
type variableName = value;

Example

This example shows how to declare variables of different types and assign values to them. It then prints their values.

java

public class Main {
    public static void main(String[] args) {
        int age = 30;               // integer variable
        double price = 19.99;       // decimal number
        String name = "Alice";    // text

        System.out.println("Age: " + age);
        System.out.println("Price: " + price);
        System.out.println("Name: " + name);
    }
}

Output

Age: 30
Price: 19.99
Name: Alice

Common Pitfalls

Common mistakes when declaring variables include:

• Forgetting the semicolon ; at the end of the declaration.
• Using a variable before declaring it.
• Choosing invalid names (like starting with a number or using spaces).
• Assigning a value of the wrong type (e.g., assigning text to an int variable).

java

public class Main {
    public static void main(String[] args) {
        // Wrong: missing semicolon
        // int number = 10;

        // Wrong: using variable before declaration
        // System.out.println(value);
        // int value = 5;

        // Wrong: invalid variable name
        // int 1stNumber = 10;

        // Wrong: type mismatch
        // int count = "five";

        // Correct way:
        int number = 10;
        System.out.println(number);
    }
}

Output

10

Quick Reference

Remember these tips when declaring variables in Java:

• Always specify the type before the variable name.
• End each declaration with a semicolon.
• Variable names should start with a letter or underscore, no spaces.
• Assign values compatible with the variable's type.

Key Takeaways

Declare variables by writing the type followed by the variable name and a semicolon.

You can assign a value during declaration using the equals sign.

Variable names must follow Java naming rules and cannot start with numbers.

Always end declarations with a semicolon to avoid syntax errors.

Assign values that match the declared variable type to prevent errors.