Declaring and naming variables¶
☕ Java 17 · Declaring Variables · 1/2
Declaration and initialization¶
A variable is a named slot in memory. Declaring it means giving its type and its name; initializing it means giving it a first value:
String title; // declaration
title = "Stranger Things"; // initialization
int releaseYear = 2016; // both on one line
double rating = 9.5;
The pattern is always: type, name, optionally = and a value, then ;.
Declaring several variables at once¶
Variables of the same type can share one declaration, separated by commas. Each one may or may not get a value:
int season, episode, duration;
int season = 1, episode, duration = 45; // only season and duration initialized
You can't mix types in one declaration:
int season, String title; // ❌ doesn't compile
int season; String title; // ✅ two separate declarations on one line (legal, but hard to read)
Which names are legal?¶
Java checks every name, or identifier, against four rules:
| Rule | ✅ | ❌ |
|---|---|---|
Starts with a letter, $ or _ |
movieTitle, _year2024, $price |
3dMovie |
Then letters, digits, $, _ only |
season2 |
my-rating (that's a minus) |
| Not a reserved word | isActive |
class, int, for |
| Not a single underscore | _count |
_ |
Names are case-sensitive: rating, Rating and RATING are three different variables.
Naming conventions¶
The compiler only enforces the rules above. Professional Java code also follows these conventions:
String streamingPlatformName = "Netflix"; // camelCase: variables and methods
class StreamingPlatform { } // PascalCase: classes
final int MAX_EPISODE_DURATION = 3600; // SCREAMING_SNAKE_CASE: constants
| Convention | Used for | Shape |
|---|---|---|
| camelCase | variables, methods | first word lowercase, next words capitalized |
| PascalCase | classes | every word capitalized |
| SCREAMING_SNAKE_CASE | constants (final) |
all uppercase, words joined by _ |
Stick to them: anyone reading your code knows at a glance what each name is.
Next, the variables you declare inside methods follow stricter rules, and two keywords change how a declaration works: final and var.