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

Abstract classes

The abstract keyword in Kotlin defines a class or a member whose implementation is missing or incomplete. Abstract classes can be extended but cannot be instantiated. Abstract classes do not have to have abstract members, but an abstract member has to be defined inside an abstract class. Let's define an abstract class that has two abstract members, a property and a function:

abstract class BaseUser {
abstract val name: String
abstract fun login()

fun logout(){
println("Logging out")

You can see that we also have one non-abstract function. Abstract classes can have state and non-abstract members. You can also see that an abstract function doesn't have an implementation, it only has a signature. The same for the abstract property, it doesn't return any value. If you had the abstract modifier on a member that has an implementation, you'd get a compiler error. This BaseUser class wouldn't compile:

abstract class BaseUser {

//compiler error
abstract val name: String =...