Java Variables

Variables in Java are used to store data values. Unlike some languages, Java requires you to declare the type of a variable before using it.

Declaring Variables

In Java, you must specify the data type when creating a variable.

Example

public class Main {
  public static void main(String[] args) {
int x = 5;
String name = "Ali";

System.out.println(x);
System.out.println(name);
  }
}

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Common Variable Types

int → stores integers (e.g., 10)
double → stores decimal numbers (e.g., 3.14)
char → stores a single character (e.g., 'A')
String → stores text (e.g., "Hello")
boolean → stores true or false

Declaring Multiple Variables

You can declare multiple variables in one line.

Example

public class Main {
  public static void main(String[] args) {
int x = 5, y = 10, z = 15;

System.out.println(x);
System.out.println(y);
System.out.println(z);
  }
}

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Final Variables (Constants)

If you do not want a variable value to change, use the final keyword.

Example

public class Main {
  public static void main(String[] args) {
final int x = 10;

// x = 20;  // This will cause an error

System.out.println(x);
  }
}

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Variable Naming Rules

Variable names must start with a letter, $, or _
They cannot start with a number
Java is case-sensitive (age and Age are different)
Do not use reserved keywords

Best Practices

Use meaningful variable names
Follow camelCase naming (e.g., userName)
Keep names short but descriptive

Using Variables in Output

Variables can be used to display dynamic information.

Example

public class Main {
  public static void main(String[] args) {
String name = "Ali";
int age = 25;

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

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