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

Local variables

Local variables can be declared in two ways: first, with the val  keyword, then they are immutable (the variable cannot be reassigned). If you are coming from Java, val would be equal to variables declared with a final keyword.

Secondly, you can declare a local variable with a var keyword; then it is considered mutable and the value can be reassigned after a declaration.

The following command demonstrates that it will not compile, because the bar local variable cannot be reassigned:

fun immutable() {
val bar: String = "Kotlin"
bar = "Kotlin is awesome" // compiler error

And, when declared with var, the compiler allows a local variable to be reassigned:

fun mutable() {
var bar: String = "Kotlin"
bar = "Kotlin is awesome" 

You should favor immutable variables. The compiler will give you a warning if you use a mutable variable but only assign it once.

Whether you declare a variable as mutable or immutable, it has to have a value when it is declared, or, if it doesn’t have a value...