Getting Started With Kotlin

In this book I assume that you’re familiar with at least one other programming language like Java or Scala, so I don’t spend much time on programming basics. That is, I assume that you’ve seen things like for-loops, classes, and methods before, so I don’t try to explain object-oriented or functional programming, I generally only write, “This is how you create a class in Kotlin,” that sort of thing.

That being said, if you’re new to Kotlin, there are a few good things to know before you jump in.

Download Kotlin

To run the examples in this book you’ll need to download the Kotlin compiler and runtime environment. Visit for information about how to use Kotlin from the command line, or in the IntelliJ IDEA, Android Studio, and Eclipse IDEs.

In this book I assume that you have the Java SDK and Kotlin command line tools installed.


Comments in Kotlin are just like comments in Java (and many other languages):

// a single line comment

 * a multiline comment

 * also a multiline comment

Naming conventions

Kotlin naming conventions follow the same “camel case” style as Java and Scala:

  • Class names: Person, StoreEmployee
  • Variable names: name, firstName
  • Method names: convertToInt, toUpper

Kotlin source files

Kotlin source code files end with the .kt filename extension.

Coding style

A few notes about the coding style in this book:

  • I indent source code lines with four spaces, but most people seem to use two spaces. I find that four spaces makes code easier to read.
  • In this book I use val variables in all places unless the feature I’m showing specifically requires the use of var. It’s a best practice to always use val unless there’s a good reason not to.

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