Variables in Java

Today let's talk about variables in Java. In Java mainly we can have four different variable types.

1. Instance Variables (Non-Static Fields)
    Instance variables are used to refer the objects(instances) of classes.

2. Class Variables (Static Fields)

    Here we use static modifier in front of the variable name and this tells the compiler that there is           exactly one copy of this variable in existence. If we use the keyword final also then that would           indicate that the value of the variable will never change.

3. Local Variables

    These variables are declared inside a method and they are only visible within that particular                  method and not accessible from the rest of the class. 

4. Parameters

    Let's take the main method as an example, public static void main(String [] args){ } ,here args            variable is the parameter to this method. And constructors also take parameter variables as                   arguments.

You may be confused by the words 'variable' and 'fields'. Local variables and Parameters are not called fields. An object stores its state in fields.

Java Variable Naming Rules

• A variable name can begin with a letter, dollar sign ($) or underscore( _ ) . But it is better not to begin with a $ or _ because some auto-generated names start with a $ sign.
• A variable name cannot begin with a digit.
• White spaces are not allowed in a variable name.
• We cannot use key words in Java as variable names.

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

When you are declaring a non-static variable it is better to use Lower CamelCase Notation for it. Start the variable name with a lower case letter and then if it consists of more than one word, capitalize the first letter of each subsequent word.

 ex: thisIsLowerCamelCase 

Constant Variable Declaration

When declaring a constant variable, the standard is to use upper case for every letter, and if it consists  of more than one word, separate them with underscore ( _ ) character.

ex: static final int START_POINT = 10 ;