# Encapsulation — Core Java

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

> Hide internal state behind Java's four access levels — private, package-private, protected, public — and expose validated getters and setters.

## Four access levels

`private` (same class), package-private (no keyword — same package), `protected` (package + subclasses), `public` (everywhere). Default to the **most restrictive** that works.

## Getters & setters

Keep fields `private` and expose controlled accessors. A setter can validate; a getter can compute. This lets the internals change without breaking callers.

```java
public class Account {
    private double balance;

    public double getBalance() { return balance; }
    public void deposit(double amt) {
        if (amt <= 0) throw new IllegalArgumentException("amt");
        balance += amt;
    }
}
```