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

Extension functions

Often, you can encounter a situation where you wish you could add some functionality to a type that you don't own. This is what extension functions enable you to do. This is a concept where you can add members (functions and properties) to a type, outside of its definition, but still call it as a normal member. Here is one such example; we'll extend the Int type and add a function that checks if it is a power of two:

fun Int.isPowerOf2(): Boolean {
return this > 0 && ((this and this - 1) == 0)

The syntax of an extension function is similar to normal functions, you just add the type that you are extending followed by the dot before the function name.

We can call the function now as a normal member:

val n = 8
val isPowerOf2 = n.isPowerOf2()

Inside the extension function, this keyword refers to the instance of the type we've extended. In our example, this keyword inside the extension function would refer to number eight.

Note that inside the extension function, you...