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

Compiling and running Kotlin

Kotlin started as a JVM language, so the first compiler for Kotlin was targeting Java bytecode. But now, there are also compilers that can turn Kotlin into JavaScript and one that is still experimental, that produces native code.

Thanks to this compiler and the native code output, soon it will be possible to write apps with Kotlin that don't require additional runtimes.

This book will focus on Kotlin running on JVM, as this is the most popular usage of Kotlin today. But most of the things learned here can also be applied to other Kotlin platforms (both JavaScript and Native).

Kotlin source code is stored in files with a .kt extension, similar to the way that Java's are stored with a .java extension. Compiling Kotlin .kt files produces .class files that contain Java bytecode.

These are the same .class files that a Java compiler produces.

From there, .class files are bundled inside .jar files to form a module (a library or an app).

Since JVM only knows about Java bytecode, running apps written in Kotlin is no different from how they are written in Java.

One additional step is needed to run Kotlin modules or apps. Kotlin has its own standard library, which builds upon Java's Standard Library, and it has to be distributed with your module or app. Luckily, the Kotlin compiler does this step for us (if you are using the compiler from the command-line, just add the -include-runtime argument to a kotlinc command). Also, with the size of around 800 KB, we can say that the Kotlin standard library is relatively small and you shouldn't be worried about it.

The following diagram shows how Kotlin source code is compiled and run on the JVM: