Java Variables

Variables are the most important part of every programming language. They holds the values to use whenever we required in the program.

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What are the variables in java?

A variable is an identifier denotes a storage location used to store a data value or a variable is a basic unit of storage. Unlike constants thay remain unchanged during the execution of a program. A variable may take different values at different times during the execution of the program.

A variable name can be selected by the programmer in a meaningful way so as to reproduce data stored in it.

Example - radian, class_value, max, PI, total_no_of_days etc

Example - int roll_number, String name, float PI etc;

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What are the rules for declaring variables in java?

Java allows us to declare variables as the programmer want. But they must follow some rules before declaration as shown below

No	Rule	Incorrect way	Correct way
1	They must not begin with a digit	0value, 18a, 5days	value0, a18, days5
2	Uppercase and lowercase are distinct	int abc; ABC = 20;	int abc; abc = 20;
3	White spaces or commas are not allowed between variables.	int my value; double max,1;	int myvalue; double max,max1;
4	It should not be a keyword	int class; float return;	int class1 or CLASS; float return_ or return1;
5	The first character must be an alphabet or underscore only.	int @a; float $profit;	int Alpha; char _data;
6	Variable names can be of any length	int ; char ;	int my_first_val; char this_varialbe_for_single_value;

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What is variable declaration mean?

Declaration means

1. It tells variable name to the compiler
2. It specifies the data types of the data hold by variable.
3. The place of declaration in the program decided the scope of the variable.

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How to declare variables in java?

Syntax

type variable_name;

OR

type variable1,variable2,variable3;

Example

int a;
float pi , percentages, radius;
double distance;

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How to assign values to the variables?

Initialization of variables

The process of giving initial values to the variables is known as the initialization. The variables are automatically initialized to zero if into assigned to any other value. A variable must be given a value after it has been declared but before it is used in an expression. It can be done in following ways.

No	Method	Example
1	By assignment statement	Int a; a = 100;
2	By calling method	Int a; a = Integer.parseInt(arg[0])

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What are the default values of variables?

Every variable has default value in java. If variable is not initialized when it is first created, java provides default value to that variables automatically as shown below.

Type of variable	Variable default value
byte	0
short	0
int	0
char	NULL
float	0.0f
double	0.0d
long	0L
Boolean	false
Reference	NULL

During execution of java program the values of variables are changed. But the constant variables which are declared as final cannot be changed. They remains as it is until end of the program.

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