Introduction to Variables and its stages in JAVA Programming

In Java, Variables represent named storage locations, whose values can be manipulated during program run. For instance, to store name of a student and marks of a student during a program run, we require storage locations that should be named too so that these can be distinguished easily. Variable called as symbolic variables (because these are named), serve the purpose.

Declaration of a variable

The declaration of a variable generally takes the following form
type variable-name;

Where type is any DataType in Java and variable-name is the variable to be used further, it is an identifier thus all rules of identifier naming apply to the name of variable. Following declaration creates a variable age of int type:
int age;

Following are some more examples of C variables declarations
double pival;
float res;

The above declaration creates a variable ‘pival’ of type double and a variable ‘res’ of type float. A simply definition consist of a type specifier followed by a variable-name. When more than one identifier of a type is being defined, a comma-separated list of identifiers may follow the type specifier. For example,
double salary, wage ;
int month, day, year ;
long distance, area ;

Initialization of Variables

All the example definitions of previous paragraph are simple definitions. A simple definition does not provide a first value or initial value to the variable i.e. variable is uninitialized and the variable’s value said to be undefined. A first value (initial value) may be specified in the definition of a variable. A variable with declaration first value is said to be an initialised variable. Java supports two form of variable definition:

int val = 1001;

Here val is initialized with a first value of 1001. Following are some more examples of initialized variables:
double price = 214.70, discount = 0.12;
float fint =0.27 F;
long val = 25;
string name = “Rohan”;

Dynamic Initialization

The expression that initializes a variables (that assign it a value for initial use) can be an expression with:
a literal
Byte a = 3
a reference to another variables e.g.
short a = 0;
short b = a ;
a call to a method, in which case the return value determines the initialization. This type of initialization is called dynamic initialization. In the below code a and b is initialized but not yet c. When program runs then c will have the value returned by the function invoked here i.e. math.sqrt().

double a =3.0, b =4.0 ;
double c = math.sqrt (a*a + b*b);

Initial Values of Variables

Every variable in a program must have a value before its value is used. Each class variable (also called Field variable), instance variable, or array components is initialized with a default value when it is created: