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

Delegated properties

We've already seen previously in Chapter 3, Classes and Object-Oriented Programming, about classes how Kotlin's by keyword can be used for class delegation. The same keyword can also be used for property delegation. As the name suggests, this concept allows a property's get or set methods to be delegated to another object. First, we’ll learn how to write a delegate, then we’ll see what delegates are included with the standard library.

Let's say we want a property that is lazily initialized, that is, initialized when accessed for the first time. We can use a delegate property for this:

private val str by lazyProperty { "I'm lazily initialized" }

The syntax for a delegate property is the by keyword, followed by an expression that returns an instance of the ReadOnlyProperty interface in the case of an immutable property, or the ReadWriteProperty interface in the case of a mutable property. This is how the interfaces are defined:

public interface ReadOnlyProperty<in R, out...