Duncan McGregor - Java to Kotlin: A Refactoring Guidebook

by Duncan McGregor and Nat Pryce

Copyright 2021 Duncan McGregor and Nat Pryce. All rights reserved.

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978-1-492-08227-9

[LSI]

Hello, this is Duncan and Nat.As youre reading this preface, youre probably trying to decide whether to invest some hours into reading the rest of this book.So lets cut to the chase:

This book wont teach you to program computers in Kotlin.

We started writing a book that would, but it soon became clear that Kotlin is a large language, and so the book was going to take longer to write than we wanted.There are also already some great books in that space, and we dont like competing against great.

We decided instead to make our lives easier by concentrating on teaching Kotlin to Java developers, based on a workshop that we run called Refactoring to Kotlin.This teaches the Kotlin language by converting existing code and is (according to our marketing material) designed for Java teams wanting to leverage their existing knowledge to accelerate their Kotlin adoption.

We started writing that book, but it soon became clear that Kotlin is still a large language, and so we would still be writing for a long time.We also found that motivated and experienced Java developers can pick up most of Kotlin very quickly.It felt patronizing to plow our way through language features that our target readers will probably just appreciate and adopt as soon as they see them.So we abandoned that idea, and as a result:

This book wont teach you the Kotlin language.

So why should you read it?Because we have written the book we wish was available when we first adopted Kotlin.We are experienced programmers who know Java and the Java ecosystem well.We hope you are too.Like us, you probably have experience in a number of other languages.Youve learned the basics of Kotlin, and you recognize that to get the best out of the language you will need to design your systems differently.You have found that some things that are cumbersome in Java are much easier in Kotlin, and that some features, such as checked exceptions, are not there at all.You dont want to end up merely writing Java code in Kotlin syntax.

Perhaps you have skin in the game.Maybe youre in a technical leadership position, or have successfully convinced your team to adopt Kotlin.You might have spent some political capital to get Kotlin into the project.Now you need to ensure that the transition goes smoothly.

You may be responsible for a Java codebase and want to ensure that introducing Kotlin wont destabilize its existing, business-critical code.Or you may be starting a Kotlin project from scratch but realize your design instincts turn more readily to Java and objects than to Kotlin and functions.

If this is you, as it was us, then youve come to the right place.This book will help you adapt your thinking and designs to take advantage of Kotlin.Thats not enough, though, because you have existing code that you need to maintain and enhance.So we also show how to migrate that code from Java to Kotlin syntax, and from Java to Kotlin thinking, incrementally and safely, using the automated refactoring tools built into the IntelliJ IDE.