The first four chapters are about objects and classes, a reasonable place to start, but you have to take into account that Chapter 7 is on control structures and that might be a better place to start. In general the material assumes that you are an object-oriented novice. but the next second the level changes to intermediate Kotlin and you are looking at hashCode(). We also look at nullable types. This is not a logical account of Kotlin's object-oriented approach.

Chapter 5 deals with collections and I think this is too early given we haven't gone over basics like control structures. The same comment applies to Chapter 6 on Generics - it just isn't this important. Most Kotlin programmers will be consumers of generic classes not producers. What a shock then to reach Chapter 7 and discover that we are back in the land of If..then..Else. and sections titled "For is for looping".

Chapter 8 deals with data classes and spends far too much time on a simple idea. Chapter 9 follows on with enums and other special classes. Chapter 10 is about functions and this is a big area where Kotlin has made things more sophisticated. Again my main concern was the lack of logical organization.

Chapter 11 is supposed to be about idiomatic Kotlin but is actually about scoped functions. Is this all there is to say about idiomatic Kotlin? Chapter 12 returns to inheritance and it deals with things that weren't covered earlier for no particular reason.

The final chapter discusses Kotlin for Android, but really doesn't say anything helpful, and then goes on to compare Java and Kotlin and explains that they can work together. As one of the huge advantages of Kotlin is that it interoperates with Java this is a little late and not really enough.

You might get the impression that I'm not happy with this book and you would be right. It isn't about applications. it is a rambling introduction to the Kotlin language. Most of the time the explanations are not particularly helpful and are mostly concerned with being cute rather than clear. This said, I can well imagine that there are readers who will want a discursive journey through some parts of the Kotlin language without too much emphasis on why Kotlin is a better Java.

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