Programming Kotlin: Create Elegant, Expressive, and Performant JVM and Android Applications

445 Pages·2019·8.941 MB·English

by  Venkat Subramaniam

Early Praise for Programming Kotlin
Venkat is someone that can take any topic and make it pleasurable and easy to
understand. In this book he will take you on an adventure of learning Kotlin in a
clear and pragmatic way, providing real-world usages, while at the same time
showing you the benefits of the language.
➤ Hadi Hariri
Developer Advocate, JetBrains
This book will open the door to the amazing world of Kotlin. You’ll be guided along
this journey by one of the most famous public speakers and educators of our day.
Have a nice Kotlin!
➤ Eugene Petrenko, PhD
Developer, Speaker, JetBrains
Enter the cave of Kotlin using this excellent book as your headlight. Gain confi-
dence in this beautiful language as a cave explorer gains self-assurance in
finding his way in a newly explored cave never seen by the human eyes before.
Explore pragmatically deeper and deeper into this modern JVM language using
the knowledge, hints, and guidelines provided by an extraordinary, experienced
programming-language enthusiast: Venkat.
➤ Tom Adam
Senior Consultant, CEO, Lambda Consulting AS
The engaging and humorous way of explaining things, as Venkat does in his talks,
is also displayed in this book. It is a very well-structured and easy-to-read guide
for everyone who is—or wants to begin—programming in Kotlin.
➤ Brian Vermeer
Developer Advocate, Snyk
Really a perfect book to get up and running, and not just hear about the hype of
Kotlin. It actually explained what’s the buzz about Kotlin. Venkat did it once more!
A must-read book, not just to get up and running with Kotlin but also to compare
what we are missing in Java.
➤ Zulfikar Dharmawan
Software Engineer, ING Bank NV
Kotlin is a very promising new language, and Venkat uses his knowledge, humor,
and clear admiration for Kotlin to create a very readable and educational book.
Venkat explains things very well, provides helpful advice, and even gives an occa-
sional laugh.
➤ Tory Zundel
Software Architect
The book is well-crafted with good, succinct examples—highly recommended for
Java developers looking to transition into Kotlin.
➤ Ashish Bhatia
Software Enginner and Blogger, ashishb.net
If you’re content with Java and see no need for null-safe traversal or first-class
delegation then put this book down; you’re not ready. Otherwise, read this book.
You will be entertained and educated simultaneously.
➤ Daniel DeGroff
CTO, FusionAuth
We've left this page blank to
make the page numbers the
same in the electronic and
paper books.
We tried just leaving it out,
but then people wrote us to
ask about the missing pages.
Anyway, Eddy the Gerbil
wanted to say “hello.”
Programming Kotlin
Creating Elegant, Expressive, and
Performant JVM and Android Applications
Venkat Subramaniam
The Pragmatic Bookshelf
Raleigh, North Carolina
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The team that produced this book includes:
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or otherwise, without the prior consent of the publisher.
ISBN-13: 978-1-68050-635-8
Encoded using the finest acid-free high-entropy binary digits.
Book version: P1.0—September 2019
Contents
Foreword . . . . . . . . . . . . . xiii
Acknowledgments . . . . . . . . . . . xv
Introduction . . . . . . . . . . . . xvii
1. Hello Kotlin . . . . . . . . . . . . . 1
Reasons to Love Kotlin 3
Why Should You Choose Kotlin? 6
Taking Kotlin for a Ride 7
Compile to Bytecode and Run 8
Compiling to Other Targets 13
Which Option to Choose? 14
Wrapping Up 14
Part I — Scripting with Kotlin
2. Kotlin Essentials for the Java Eyes . . . . . . . 19
Less Typing 20
Sensible Warnings 24
Prefer val over var 26
Improved Equality Check 28
String Templates 29
Raw Strings 30
More Expressions, Fewer Statements 33
Wrapping Up 35
3. Working with Functions . . . . . . . . . . 37
Creating Functions 38
Default and Named Arguments 43
vararg and Spread 46
Contents • viii
Destructuring 49
Wrapping Up 51
4. External Iteration and Argument Matching . . . . . 53
Range and Iteration 54
Iterating over Arrays and Lists 57
When It’s Time to Use when 58
Wrapping Up 62
5. Using Collections . . . . . . . . . . . 63
Flavors of Collections 63
Using Pair and Triple 66
Arrays of Objects and Primitives 68
Using List 70
Using Set 72
Using Map 73
Wrapping Up 75
6. Type Safety to Save the Day . . . . . . . . . 77
Any and Nothing Classes 78
Nullable References 80
Type Checking and Casting 87
Explicit Type Casting 91
Generics: Variance and Constraints of Parametric Types 93
Reified Type Parameters 101
Wrapping Up 104
Part II — Object-Oriented Kotlin
7. Objects and Classes . . . . . . . . . . 107
Objects and Singletons 107
Creating Classes 113
Companion Objects and Class Members 124
Creating Generics Classes 127
Data Classes 129
Wrapping Up 132
8. Class Hierarchies and Inheritance . . . . . . . 133
Creating Interfaces and Abstract Classes 134
Nested and Inner Classes 138
Inheritance 140