Java Keywords & Identifiers

This guide explains what keywords and identifiers are in Java, their rules, best practices, and examples. It’s beginner-friendly, interview-ready, and optimized for Google ranking.

What Are Keywords in Java?

Keywords are reserved words in Java that have a special meaning in the language.
You cannot use keywords as names for variables, classes, methods, or identifiers.
Java has 52 keywords (depending on version) and 5 reserved literals like true, false, null.

List of Java Keywords (Java 17)

Keyword	Keyword	Keyword	Keyword
abstract	assert	boolean	break
byte	case	catch	char
class	const*	continue	default
do	double	else	enum
extends	final	finally	float
for	goto*	if	implements
import	instanceof	int	interface
long	native	new	package
private	protected	public	return
short	static	strictfp	super
switch	synchronized	this	throw
throws	transient	try	void
volatile	while	yield	record
sealed	permits	non-sealed	var
module	open	requires	exports

⚠️ const and goto are reserved but not used in Java.

What Are Identifiers in Java?

Identifiers are names you give to classes, methods, variables, and other elements in Java.
They help uniquely identify these program elements in your code.

Rules for Identifiers

Must start with a letter, $, or _.
Can contain letters, digits, $, or _.
Cannot be a keyword.
Java is case-sensitive (age ≠ Age).
No spaces or special characters allowed.

Valid & Invalid Identifiers Examples

Valid Identifiers	Invalid Identifiers
`int age;`	`int 2age;` // starts with digit
`String studentName;`	`String student-name;` // invalid char
`double _salary;`	`int class;` // keyword

Naming Conventions (Best Practices)

Element	Convention	Example
Class	PascalCase	`StudentDetails`
Method	camelCase	`calculateSalary()`
Variable	camelCase	`totalSalary`
Constant	UPPERCASE	`MAX_AGE`
Package	lowercase	`com.example.project`

Following conventions improves readability, collaboration, and maintainability.

Example Program Using Keywords & Identifiers

public class Student {

    // Instance Variables (Identifiers)
    String studentName;
    int age;
    final double PI = 3.14159; // Constant

    // Method
    public void displayInfo() {
        System.out.println("Name: " + studentName);
        System.out.println("Age: " + age);
        System.out.println("PI Value: " + PI);
    }

    public static void main(String[] args) {
        Student s1 = new Student();
        s1.studentName = "John";
        s1.age = 25;
        s1.displayInfo();
    }
}

Output:

Name: John
Age: 25
PI Value: 3.14159