Encapsulation

The Big Picture

Encapsulation hides internal state behind private fields and public methods. Protects invariants and decouples impl.

• "Black box" design - users don't see internals
• Prevents invalid state (negative age, null fields)
• Allows changing internals without breaking clients

Foundation of maintainable, safe code.

How It Works

The compiler enforces access modifiers: private, protected, package-private, public. Reflection can bypass (opt-in).

• Getters/setters provide controlled access
• Immutable classes (final fields) maximize safety
• Defensive copies prevent reference leaks
• JVM also performs access checks at runtime

In the Java Landscape

JavaBeans convention uses get/set method naming.

• Records (Java 16+) auto-generate accessors
• Lombok @Getter/@Setter reduces boilerplate
• Modules (Java 9+) encapsulate entire packages
• Sealed classes restrict who can subclass/implement a type
• Builder pattern for complex object construction

Pitfalls and Best Practices

• Default to private, widen only when needed
• Return copies of mutable collections, not originals
• Validate in setters: throw IllegalArgumentException
• Avoid public fields except constants (static final)
• Use builder pattern for complex construction