Book Image

Kotlin Quick Start Guide

By : Marko Devcic
Book Image

Kotlin Quick Start Guide

By: Marko Devcic

Overview of this book

Kotlin is a general purpose, object-oriented language that primarily targets the JVM and Android. Intended as a better alternative to Java, its main goals are high interoperability with Java and increased developer productivity. Kotlin is still a new language and this book will help you to learn the core Kotlin features and get you ready for developing applications with Kotlin. This book covers Kotlin features in detail and explains them with practical code examples.You will learn how to set up the environment and take your frst steps with Kotlin and its syntax. We will cover the basics of the language, including functions, variables, and basic data types. With the basics covered, the next chapters show how functions are first-class citizens in Kotlin and deal with the object-oriented side of Kotlin. You will move on to more advanced features of Kotlin. You will explore Kotlin's Standard Library and learn how to work with the Collections API. The book finishes by putting Kotlin in to practice, showing how to build a desktop app. By the end of this book, you will be confident enough to use Kotlin for your next project.
Table of Contents (15 chapters)
Title Page
Copyright and Credits
Dedication
Packt Upsell
Contributors
Preface
Index

Sealed classes


If you have experience with C#, then the sealed keyword might be confusing to you. C# uses the sealed keyword to prevent inheritance from a class, the same way Java uses final when declaring a class. Sealed classes in Kotlin are used to define restricted class hierarchies.

Sealed classes are similar to enum classes; you use them to define a fixed set of options. But unlike enum classes, where each constant is a single instance, sealed classes can have multiple instances for each option.

This restricted class hierarchy can be really useful when used with when expressions.

Here's an example of a sealed class hierarchy used with a when statement:

sealed class SuperHero

class Hulk: SuperHero() {
fun smashOpponent() {

    }
}
class SuperMan : SuperHero() {
fun flyToKrypton() {

    }
}
class SpiderMan : SuperHero() {
fun useSpiderSense() {

    }
}
fun actOnHero(hero: SuperHero) {
when (hero) {
is Hulk -> {
hero.smashOpponent()
        }
is SuperMan -> {
hero.flyToKrypton(...