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Note that you can read the main content of this book online at https://typealias.com/start. By purchasing this Leanpub edition, you'll get a PDF of the book, which you can read offline and mark up with your favorite PDF application. Plus, you'll be supporting the author!

Who is this book for?

If you’re interested in learning Kotlin development, this book is for you. Everyone has a unique experience - some readers are new to software development entirely, some are new to Kotlin development, and some are existing Kotlin developers who want a deeper understanding of certain language concepts.

My approach in this book is to explain Kotlin programming concepts with simple, tangible, and illustrated examples, so that regardless of your experience level, things will make sense. I do my best to define terms clearly before using them, so that each chapter builds upon a solid foundation of knowledge from the previous chapters.

Even if you already know some of the concepts presented in this book, my goal is to give those concepts such a fun and vivid presentation that you’ll enjoy reading about them again! I hope that will give you a definite clarity about them, shining light on the foggy corners of concepts that you might have wondered about.

Release Notes

v1.0.0 - April 9, 2025

I'm pleased to announce that Kotlin: An Illustrated Guide has arrived at its official 1.0 release! An enormous thank-you goes out to all of you who have purchased the PDF edition - your support has made it possible for me to create semi-weekly videos, as well as the new paperback edition on Amazon. Thank you for all of your support and encouragement! I hope you enjoy the book!

v1.0.0-RC3- March 24, 2025

The third release candidate updates a few illustrations and annotated code listings for clarity, legibility, and consistency—mostly ensuring colors work for both PDF and the upcoming print edition. The preface and acknowledgments sections had some minor revisions.

Good news—the table of contents now includes the chapter numbers in addition to the titles! For example, previously there was a heading in the table of contents for \"Enum Classes\" but now it says \"Chapter 5 • Enum Classes\".

The cover has been updated to match that of the print edition, and it now also includes the back cover.

v1.0.0-RC2- March 17, 2025

The second release candidate is here! It fixes a handful of typos in Chapters 17-20, corrects a few spots where a code listing had the wrong font weight, and makes a few small changes to bring it into alignment with the upcoming print edition.

v1.0.0-RC1- February 28, 2025

The first 1.0 release candidate is here! This version is similar to the previous version, but includes a few small layout updates and minor clarifications. We'll bake this version for a few weeks, and either follow it up with another release candidate or we'll mark this version as the official 1.0.

In the meantime, I'm actively working on the print edition, which will be very similar to the PDF edition, but will include a some layout and color changes to work better in print. If you're interested in the print edition, join the waitlist at https://print.typealias.com.

v1.0.0-alpha - February 20, 2025

The 1.0 alpha release includes tons of updates:

New sections introducing println() and main() in Chapter 2.
New sections introducing singleton objects and packages in Chapter 4.
Appendix A - How to run the code listings in this book.
Appendix B - How to add dependencies to Gradle and Maven projects.
Now that the main content is basically complete, the layout has settled. It's much more pleasant to read now!
Found a few terms that needed to be explained before using them. Those explanations have been added now.

The book is undergoing a few more rounds of proofreading and minor edits. Be on the lookout for a release candidate soon!

v0.21.0 - January 10, 2025

Cleaned up and standardized some of the illustrations for a consistent look throughout. I'll be incorporating the last of the reader feedback soon, so if you have any remaining comments or suggestions for me, please use the feedback link at the top of any page. Thanks!

v0.20.20 - December 23, 2024

Chapter 20 now has its full-resolution illustrations.

v0.20.19 - December 12, 2024

Chapter 19 now has its full-resolution illustrations.

v0.20.18 - December 9, 2024

Chapter 18 now has its full-resolution illustrations.

v0.20.17 - December 3, 2024

Chapter 17 now has its full-resolution illustrations.

v0.20.16 - November 24, 2024

Chapter 16 now has its full-resolution illustrations.

v0.20.15 - October 24, 2024

Chapter 15 now has its full-resolution illustrations.

v0.20.14 - October 21, 2024

Chapter 14 now has its full-resolution illustrations.

v0.20.13 - October 18, 2024

Chapter 13 now has its full-resolution illustrations.

v0.20.8 - v0.20.12 - October 10, 2024

Chapters 8-12 now have their full-resolution illustrations.

v0.20.7 - October 4, 2024

Chapter 7 now has its full-resolution illustrations.

v0.20.6 - October 1, 2024

Chapter 6 now has its full-resolution illustrations.

v0.20.5 - September 10, 2024

Chapter 5 now has its full-resolution illustrations.

v0.20.4 - September 6, 2024

Chapter 4 now has its full-resolution illustrations.

v0.20.3 - September 4, 2024

Chapter 3 now has its full-resolution illustrations.

v0.20.2 - September 3, 2024

Chapters 1-2 now have their full-resolution illustrations.

v0.20.1 - June 25, 2024

Chapter 20: Coroutine Essentials - Incorporated feedback from readers, and added captions to all code listings.

v0.20.0 - June 18, 2024

Chapter 20: Coroutine Essentials - This chapter has been promoted out of draft.

v0.20.b - June 8, 2024

Incorporated some reader feedback, and updated some illustrations in Chapter 20.

v0.20.a - May 17, 2024

Chapter 20: Coroutine Essentials - A draft of this chapter is now available.

v0.19.0 - April 19, 2024

Chapter 19: Generic Variance - Promoted out of draft, with full illustrations and edits.

v0.19.b - March 26, 2024

Chapter 18: Generics - Incorporated reader feedback, and fixed a few incorrect code listing numbers.

v0.19.a - March 19, 2024

Chapter 19: Generic Variance - This chapter is now available in draft form.

v0.18.0 - March 15, 2024

Chapter 18: Generics - This chapter has its full illustrations now, and has been promoted out of draft.

v0.18.b - March 6, 2024

Added table-of-contents bookmarks for the PDF, so that you can easily jump to a chapter from anywhere in the book. Eventually a bookmark will also be included for each top-level section under each chapter, but for the moment they're included only at the chapter level.

v0.18.a - February 19, 2024

Chapter 18: Generics - Draft version of this chapter has been published.

v0.17.0 - February 16, 2024

Chapter 17: Handling Runtime Exceptions - This chapter is now fully illustrated, and has been promoted out of draft.

v0.17.a - January 15, 2024

Chapter 17: Handling Runtime Exceptions - Draft version is now included. Let me know what you think about it via the feedback link at the top of each page!

v0.16.0 - January 10, 2024

Chapter 16: Sealed Types - Revisions and illustrations are completed and this chapter is now promoted out of draft.

v0.16.b - December 14, 2023

The feedback link was confusing for readers who hadn't already signed up for this book's discussion forum on Leanpub, so I moved the feedback to a new URL.

In order to be able to create a print edition of the book in the future, the pages had been set up for a wider inner margin, which is needed to accommodate the binding in a printed book. This made for a less optimal reading experience in a PDF, though, since the content on even pages was farther to the left, and the content on odd pages was farther to the right. In this version, I've centered the content, so that it's spaced consistently from page to page.

v0.16.a - December 13, 2023

Chapter 16: Sealed Types - Published in draft form, and ready to receive feedback.

v0.15.0 - November 14, 2023

Initial Leanpub edition, with the 15 chapters that have been previously published at https://typealias.com/start.

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