Rules For Variable Declaration in Java

Last Updated : 15 Jun, 2022

Variable in Java is a data container that saves the data values during Java program execution. Every variable is assigned a data type that designates the type and quantity of value it can hold. Variable is a memory location name of the data. A variable is a name given to a memory location. For More On Variables please check Variables in Java.

Syntax:

data _type variable_name = value;

Rules to Declare a Variable

A variable name can consist of Capital letters A-Z, lowercase letters a-z digits 0-9, and two special characters such as _ underscore and $ dollar sign.
The first character must not be a digit.
Blank spaces cannot be used in variable names.
Java keywords cannot be used as variable names.
Variable names are case-sensitive.
There is no limit on the length of a variable name but by convention, it should be between 4 to 15 chars.
Variable names always should exist on the left-hand side of assignment operators.

List of Java keywords

abstract	continue	for	new	switch
assert	package	synchronized	default	goto
boolean	do	if	private	this
break	else	import	public	throw
byte	enum	implements	protected	throws
case	double	instanceof	return	transient
catch	extends	int	short	try
char	final	interface	static	void
class	finally	long	strictfp	volatile
const	float	native	super	while

The table above shows the list of all java keywords that programmers can not use for naming their variables, methods, classes, etc. The keywords const and goto are reserved, but they are not currently used. The words true, false, and null might seem like keywords, but they are actually literals, you cannot use them as identifiers in your programs.

Example

Java

import java.io.*;
 
class GFG {
    public static void main(String[] args)
    {
        // Declaring all the
        // possible combinations of
        // variable format
        int _a = 10;
        int $b = 20;
        int C = 30;
        int c = 40;
 
        int result = _a + $b + C + c;
 
        // Displaying O/P
        System.out.println("Result: " + result);
    }
}