JAVA Variable stores,
retrieve and manipulate information. A variable reserve some space in computer
memory in order to store the information. A variable can be defined and then
assigned it a value in some later stage or it can be assigned some value while
declaring the variable at the same time.
It is called initialization of the variable and value assigned to the
variable at that time is called default value.
In order to define
the variables in JAVA we need two things one is Data Type and other is name of
the variables, Below is the examples of three variables where rollnumber, name
and sal are variable and int,char and double are the data types of these
variable.
int rollnumber = 3;
char name = 'X';
double sal;
datatype define the
type of the data that can be stored or assigned to variable e.g rollnumber can
only stores INTERGER values, name can only stores single CHARACTER value and
sal can stores a decimal value.
There are few rules
for while naming variable in JAVA.
1. A variable name should be meaningful
2. JAVA is case sensitive, so that it
differentiate between upper and lower case letters
3. A variable cannot be started with digit or
special symbols like %,#,@ etc and we cannot use them inside the these while
naming the vaiables.
4. A variable name can contains only letters,
digits and underscore
5. Keywords cannot be used in order to name
the variables. Keywords are specific constants which have specific meaning and
task in the Computer Language and defined by the compiler of the language.
6. It is good practice to use camel case
naming while writing variable names for example
int RollNumber = 3;
char Name = 'X';
double AnnualSal;
Types Of Variables
in JAVA:
There are 3 types of variables in JAVA:
1. Local Variable
2. Instance variable
3. Class Variable/Static variable
2. Instance variable
3. Class Variable/Static variable
Local variable:
- These are also called as stack variable. Because they exist in stack memory
- It is mandatory to initialize the local variable. Otherwise you will get run time error from compiler
- These can be defined inside method, constructor or also inside block. The scope or life time of local variable destroyed with end of method completion.
Instance variable:
- Instance variable are also known as member variable or field
- These are associated with the object creation. As the object get created instance variable also get created
- These live on heap memory. In case, if you don’t initialize instance variable with initial value these get default value at run time implicitly.
Class Variable/Static Variable:
- These are loaded and initialized when class is loaded in JVM
- There exists only one copy of class variable
- They live on heap memory. If these variables are not initialized to some default value is assigned to them implicitly.
