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

Working with collections

The standard library in the kotlin.collections package offers numerous extension functions that extend the collections types. Most of them extend the base Iterable interface, so they can be used with any collection type. 

The library is too big to cover every function, so we’ll see here the most useful ones. We can group them based on their operation.

Filtering functions

These functions are used to remove or filter items from a collection.


Drop removes first n elements from the collection.

val numbers = listOf(1, 2, 3, 4, 5)
val dropped = numbers.drop(2)

The dropped list now contains [3, 4, 5].


Filter applies the supplied predicate function to the collection and returns the following result:

val numbers = listOf(1, 2, 3, 4, 5)
val smallerThan3 = numbers.filter { n -> n < 3 }

The resulting list has these numbers [1, 2].


This is the inverted filter function:

val numbers = listOf(1, 2, 3, 4, 5)
val largerThan3 = numbers.filterNot { n -> n < 3 }