Variables and identifiers

Variables and identifiers

Variables

A variable is a named memory location that holds a value. In Java, every variable has a type that determines what kind of data it can store.

Variable declaration syntax:

type identifier [ = value ];

Example:

int age;
double salary = 45000.50;
char grade = 'A';
boolean isActive = true;

Identifiers

Identifiers are names given to variables, methods, classes, packages, etc. Java has strict rules for identifiers:

• Can contain letters, digits, underscores (_), and dollar signs ($).
• Must not start with a digit.
• Are case‑sensitive (age and Age are different).
• Cannot be a reserved keyword (like int, class, public).

Valid identifiers:

int score;
double _price;
String $name;
int counter1;

Invalid identifiers:

int 1stPlace;   // starts with a digit
double class;   // 'class' is a keyword
String my-name; // hyphen not allowed

Naming conventions (recommended):

• Variables and methods: camelCase (e.g., studentName, calculateTotal())
• Classes: PascalCase (e.g., Student, BankAccount)
• Constants: UPPER_SNAKE_CASE (e.g., MAX_VALUE, PI)