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
Packt Upsell


To cast from one type to another, Kotlin uses the as keyword. Here’s how you would cast Any type to an Int type:

fun casting(any: Any) {
val num = any as Int

During runtime, before casting, the JVM will check if the source type can be cast to target type. If not, ClassCastException will be thrown.

Safe casting

There is also the safe casting operator, as?. This operator checks, before casting, whether or not types are compatible. If they are, then it works as a normal asoperator. If not, a null value is assigned. Notice how in this example, the local variable num has to be declared as a nullable type:

fun safeCasting(any: Any) {
val num: Int? = any as? Int

Safe casts can be used with all other null handling operators (safe call, non-null assertions, and Elvis), but Elvis is probably the most useful one. Together they can be used to do a non-null try-cast operation, like this example shows:

fun safeCastingWithElvisl(any: Any) {
val num: Int = any as? Int ?: 0