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

Smart casts

If you are wondering how, in the previous section, we called functions that belong to supertypes from the base SuperHero type, and the compiler did not complain, the answer is the smart casting feature of the Kotlin compiler. Whenever you check in an ifor a whenstatement that a type can be cast to another type, the compiler then allows you to access all members from the target type,that is,the compiler does the cast for you. Let's say we have a class hierarchy like the following one:

open class BaseUser(val name: String)

open class User(name: String,
val birthYear: Int) : BaseUser(name) {
fun login() {
open class AdminUser(name: String,
                     birthYear: Int) : User(name, birthYear) {
fun accessLogs() {

We have a function that accepts the base type; we can check with the is keyword whether a type is an instance of another type. When the compiler knows that a type is actually an instance of a different type, you can immediately access all the members...