Foreword

With this book, you are going to learn Kotlin. On behalf of the Kotlin team I say: welcome!

Back in 2010, when we started Kotlin, we thought of it as a tool for Java developers to let them build what they want with ease and pleasure. We bet on type safety for excellent tooling and early detection of programming errors. We bet on interoperability with Java to give all Kotlin developers access to the vast Java ecosystem. Nowadays, Kotlin is a multiplatform language that can run on a server running JVM, on an Android device, in a web browser, on an iOS device or a Linux machine or even a microcontroller. Yet, our principles stayed the same: we let people build software with ease and pleasure, and we bet on tooling, interoperability with every platform, and on catching errors early.

Language development has multiple stages. First, you just have an idea, and at that stage I was full of doubt and at the same time was very eager to try. One can call this faith, maybe. Then you have your first program compile and run. It’s starting to take some shape. Then it grows. Then you fix a lot of problems. And more problems. Then if you are lucky somebody outside your team gets excited about your language, and you are in heaven. Early adopters come and give you feedback. Then more problems, and a lot of doubt: are we ready to release? Then you just can’t wait any longer, you double down on it and release 1.0. You celebrate briefly and rush to fix all the issues that the new users reported. Some time goes by, the ecosystem grows, the team grows, more users, some new features, new releases, more bugs, people write bigger projects… Then an author who was well known before you even started writes a book about your language. I am here. It’s a good feeling :).

As this book assumes some knowledge of Java, you’ll start where we started, and when you get to the end of the book you’ll have a very good picture of the language and its practical applications within the JVM world and Android. You’ll know how to do what you want with Kotlin and how it can help you. My goal as the language designer is to make Kotlin useful to you, and Venkat has done a great job of making it enjoyable to learn.

I wish you a good time with this book. Have a nice Kotlin!

Andrey Breslav

Lead Designer of Kotlin

July, 2019