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

Class constructors

In Kotlin, class constructors can be defined in two ways, as primary and as secondary constructors.

Primary constructors

Kotlin has two ways of declaring a constructor. In the example of the User class, we had a primary constructor. Primary constructors are declared with parentheses after the class name, in the class header.

Specifying the constructor keyword is optional if the constructor doesn't have visibility modifiers or annotations.

Constructors can have parameters, but cannot have any initialization code in them. The Java User class constructor has both parameters and initialization code. Initialization code was needed because the private fields needed to be initialized with values from constructor arguments.

The same code was not needed in Kotlin, because Kotlin allows properties to be declared inside the constructor. When declared like this, they become both properties and constructor parameters. The Kotlin compiler then emits bytecode that resembles the Java user...