Java Variables

A variable is a name given to a memory location. It is the basic unit of storage in a program. The value stored in a variable can be changed during program execution. In Java, all the variables must be declared before use.

1. Declaring variables

datatype: Type of data that can be stored in this variable.
variable_name: Name given to the variable.

Syntax:


data_type variable_name;

Example:


char alphabet ;
int number;

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Where alphabet and number are then variables of type character and integer.

2. Assigning values to variables

Values can be assigned to a variable directly using assignment operator(=).

Syntax:


data_type variable_name = value;

Example:‍


char alphabet = 'A';
int number = 100;

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Where A and 100 are the values assigned to the variable alphabet and number.

3. Rules for Naming Variables

Variable names may consists of alphabets , digits , underscore ( _ ) and dollar sign ( $ ).
They must not be begin with digits.
It should not be a keyword.
White space is not allowed.
Variable names can't be in length.
Uppercase and Lowercase are distinct.

Valid and Invalid Variable Names :


int sum_value = 10; // ✔️ valid ( underscores are allowed )
int $value = 20;    // ✔️ valid ( dollor sign is allowed )
int 12sum = 10;     // ❌ invalid ( variable name can not start with digits )
int break = 20;     // ❌ invalid ( variable names should not be a keyword )
int sum value = 30; // ❌ invalid ( whitespace is not allowed )

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