Kotlin in Action

Chapter 4. Classes, objects, and interfaces

This chapter covers

• Classes and interfaces
• Nontrivial properties and constructors
• Data classes
• Class delegation
• Using the object keyword

This chapter gives you a deeper understanding of working with classes in Kotlin. In chapter 2, you saw the basic syntax for declaring a class. You know how to declare methods and properties, use simple primary constructors (aren’t they nice?), and work with enums. But there’s more to see.

Kotlin’s classes and interfaces differ a bit from their Java counterparts: for example, interfaces can contain property declarations. Unlike in Java, Kotlin’s declarations are final and public by default. In addition, nested classes aren’t inner by default: they don’t contain ...