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

Kotlin standard library functions

The library provides a lot of useful functions for easier usage of the language and common programming tasks. We'll explore the contracts (preconditions) functions and the so-called standard functions.


In the base Kotlin package, you can find several functions that can be used for runtime checking of data. They can be used for defining preconditions in functions. If you ever coded in Java then you probably wrote a not null precondition, with checking that an argument passed to a method is not null. The following methods are available, check, checkNotNull, require, requireNotNull and error. Let’s show some examples of them.


This function accepts a boolean condition and if it evaluates to false it will throw an IllegalStateException:

check(str.length > 5) { "Minimum length is 5" }


This function accepts a nullable argument, and, if it is null, throws an IllegalStateException. Otherwise, it returns the same argument as a non-nullable...