What is Variable in JAVA ?

 What is Variable in JAVA ?

• It is a name of storage space which is used to store data.
• It's value may be changed.
• It always contains last value stored to it.
• It is always declared with data type.

    

Variables store data for processing.
A variable is given a name (or identifier), such as area, age, height, and the like. The name uniquely identifies each variable, assigning a value to the variable and retrieving the value stored.

Variables have types. Some examples:
- int: for integers (whole numbers) such as 123 and -456
- double: for floating-point or real numbers with optional decimal points and fractional parts in fixed or scientific notations, such as 3.1416, -55.66.
- String: for texts such as "Hello" or "Good Morning!". Text strings are enclosed within double quotes.

You can declare a variable of a type and assign it a value.
Example:

String name = "David";

JAVA

This creates a variable called name of type String, and assigns it the value "David".

It is important to note that a variable is associated with a type, and is only capable of storing values of that particular type. For example, an int variable can store integer values, such as 123; but it cannot store real numbers, such as 12.34, or texts, such as "Hello"

Variable Declaration

int rollno;
float marks;
char grade;

• Here rollno is a variable of type int ,marks is a variable of type float and grade is a variable of type char.

Variable Initialization

• We can initialize a variable at the time of declaration of variable or after declaration.

int rollno=201;
float marks=85.6;
char grade='A';

• Here 201 is the value of rollno,85.6 is the value of marks and A is the value of grade. Character value is always written in single quotes.

Other method of variable Initialization

• We can also initialize a variable after the time of declaration of variable.

int rollno;
float marks;
char grade;

rollno=201;
marks=85.6;
grade='A';

Rules to define a variable

• The first letter of a variable should be alphabet or underscore(_).
• The first letter of variable should not be digit.
• After first character it may be combination of alphabets and digits.
• Blank spaces are not allowed in variable name.
• Variable name should not be a keyword.

Types of Variable

• Local Variable
• Instance Variable
• Static Variable

Local Variable

• A variable declared inside the body of the method or constructor or block is called local variable.
• Local variable can be used only inside that method/function in which it is declared.
• A local variable can be a static variable.

class Easy
{
 public void add()
 {
 int x,y=10,z=20;//declaring local variable
 x=y+z;
 System.out.println("Add="+x);
 }
 public static void main(String[] args) 
 {
  Easy obj=new Easy();
  obj.add();       
 }
}
/*
### Output ###
Add=30
*/

Instance Variable

• A variable which is declared inside a class but outside the body of the method or constructor or block is called instance variable.
• Instance variable can be used anywhere in the program.

class Easy
{
 //these instance variabe can be used 
 //inside all the function of this class
 int x,y=30,z=20;
 public void add()
 {
 x=y+z;//accessing instance variable
 System.out.println("Add="+x);
 }
 public void sub()
 {
 x=y-z;//accessing instance variable
 System.out.println("Sub="+x);
 }
 public static void main(String[] args) 
 {
  Easy obj=new Easy();
  obj.add();  
  obj.sub();
 }
}
/*
### Output ###
Add=30
Sub=10
*/

Static Variable

• A variable which is declared with static keyword, inside a class but outside the body of the method or constructor or block is called static variable.
• Static variable is stored in the static memory.
• Static variables are created when the program starts and destroyed when the program stops.
• Static variable can be called by class name directly.

class Easy
{
 //declaring static variable
 static String text="You are a smart guy.";
 public static void main(String[] args) 
 {
     System.out.println(Easy.text);
 }
}
/*
### Output ###
You are a smart guy.
*/