Java Variable Types and Rules for Declaring Variables

Variable is nothing it is just the name of memory location.
While declaring variables we must follow rules given below.

1. Variable name must bound with data type. It means while
declaring a variable we must specify its data type.

Ex: int x=10;

2. Reserve word or keywords cannot be taken as a variable
name.

3. C
supports 32 character long variable names while in Java the length of variable
name can be infinite.

4. Nothing except 0-9, A-Z, a-z, _, $ can be used in variable
name.

5. Variable name must not start with numeric and special
characters are also not allowed.

Example:

intabc=7; (valid)

int _abc=8; (valid)

int abc8=9; (valid)

int 8abc=10 (invalid)

int $_abc=12; (valid)

int $_abc*=15; (invalid)

6. Variable name should be meaningful.

Example:

string i=”Raj”; 
//valid but not meaningful

string name=”Raj”; //valid and meaningful

Note: Local variables must be initialized before first use.

class demo

{

                public
static void main(String…s)

                {

                                int
x;      //must be initialized

                                System.out.println(x);

                }

}

There are three types of variables in Java that are
instance, local and static.

Instance variables are declared in a class, but outside any
method, constructor or block.

Local variables are declared in methods, constructors or
blocks. It must be initialized before first use.

Static variables are declared with the static keyword in a class, but outside any method, constructor or block.

class A

{

                int
x=12;               //instance variable

                staticint
y=13;    //static variable

               

                public
static void main(String…s)

                {

                                int
z=30;               //local variable

                                System.out.println(x);

                                System.out.println(y);

                                System.out.println(z);

                }

}