Although it starts from some very basic ideas, this is not a non-programmer's book. You probably don't have to program in Java to get something out of this book, but you do need to be able to program in some modern, object-oriented, language. Kotlin is a better Java and there is a tendency to explain what it does by pointing out what it does differently to Java.

The book is divided into two parts:

Introduction to Kotlin

• Kotlin basics
• Defining and calling functions
• Classes, objects, and interfaces
• Programming with lambdas
• The Kotlin type system

Embracing Kotlin

• Operator overloading and other conventions
• Higher-order functions: lambdas as parameters and return values
• Generics
• Annotations and reflection
• DSL construction

It has to be said that there isn't a great deal of difference between the two parts of the book and they feel more like simple topics and more advanced topics. However, there isn't much in the way of logical progression of completeness. This is more like a collection of topics that stand out as being different from the way Java does things. This is fine, especially as the topics are explained well and you do need to know about them. Don't expect a traditional textbook that progresses in a logical way to cover most of the language.

The explanations are good and they provide a starting point, but many of the discussions don't take us very far from what is presented in the online documentation. If you are looking for an investigation of what impact the way that Kotlin does things has on how you program then you will be disappointed. It is also clear that the authors are very pro-Kotlin and as such there are few places where deficiencies of the language are pointed out. Kotlin may be better than Java, but the need to stay compatible with the language means that it sometimes has to do things in non-optimal ways.

This isn't the perfect book on Kotlin, but it is well worth having as long as you read it as a collection of topics rather than a logical progression. If you are thinking about switching from Java to Kotlin it will help and repay the money you spend on it.

• Mike James is the author of two Kotlin titles. The Programmers Guide To Kotlin is for programmer's in any object-oriented language who wants to takes a more linear approach to discovering why Kotlin is better. Android Programming in Kotlin: Starting With An App is for programmer's who want to get into Android programming using Android Studio 3.

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