# Variables & Types — Core Java

Source: https://www.geekswithgeeks.com/en/core-java/java-variables

> Understand Java's primitive and reference types, declaring variables, final, local type inference with var, and wrapper classes with autoboxing.

## Two kinds of types

**Primitives** hold a value directly: `byte short int long float double char boolean`. **Reference types** (classes, arrays, interfaces) hold a reference to an object on the heap; their default value is `null`.

## Declaring

Types are fixed at declaration. `var` (Java 10+) infers the type of a **local** variable from its initializer — it is still statically typed, not dynamic.

```java
int count = 10;
double price = 19.99;
boolean active = true;
String name = "Ada";
var total = count * price;   // inferred as double
final int MAX = 100;        // cannot be reassigned
```

## Wrapper classes

Each primitive has an object wrapper (`int` → `Integer`, `double` → `Double`). **Autoboxing** converts between them automatically, but boxed values can be `null` and comparing them with `==` compares references — use `.equals()` or `.intValue()`.