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

Overriding members

Reimplementing functions or properties from a base type is called overriding. Overriding is also a way to achieve polymorphism, another aspect of object-oriented programming. In Kotlin, you can override them only if the base type allows it. By default, all members in Kotlin are final, that is, cannot be overridden. To allow a subclass to override a member, it has to have the open keyword. This is in contrast to Java, where by default every member is overridable. Another difference from Java is that whenever you are overriding a member, you have to have the override keyword present. Java doesn't have such a keyword and overriding is considered with just declaring a function with the same name and signatures as the base type. This can be error-prone and that's why Java uses the @Override annotation to make the developer's intentions clearer:

open class Base {
open fun print() {
println("I'm called from the base type")

class Derived : Base() {
override fun print(...