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

Object keyword

Kotlin has an object keyword, which combines both declaring a class and creating an instance of it in one action. It can be used in three different situations and has three different meanings. Let's take a look at all of them:

  • Object declaration: Defines a singleton class.
  • Companion object: Defines a nested class that can hold members related to the outer containing class. These members can't require an instance of the outer class.
  • Object expression: Creates an instance of the object on the fly, the same as Java's anonymous inner classes.

Singletons with object keyword

Sometimes, your program has to have only one instance of a certain type. This pattern is known as a singleton. In other languages, you would have to implement this pattern manually, making sure that only one instance of your type gets created. But, Kotlin has language support for creating singletons with the object keyword. Here is an example:

object Singleton {
fun sayMyName() {
println("I'm a singleton")