Kotlin supports top-level variables, you don’t need to declare them in a class. Just like Java, Kotlin is a statically typed language, but the compiler is able to determine the type from the context, this is called type inference: val hello: String = 'Hello' // explicit type val hello = 'Hello' // inferred type val i = 42 // Int val l = 42L // Long val d = 42.0 // Double val f = 42f // Float The variable type may come after the name, separated by a colon. Kotlin’s variable declaration starts with one of the two keywords above, followed by the variable name. Val i = 42 // final variable var j = 42 // mutable variable The value of such variable can be changed.

A val variable can’t be reassigned after initialization and corresponds to a final variable in Java. In Kotlin, there are two keywords to declare a variable: However, it’s still a good practice to follow Java’s directory layout, while not hesitating to group multiple classes into the same file if they’re small and related. Unlike Java, Kotlin doesn’t impose any restrictions on the layout and naming of source files: you can put multiple classes in the same file, and choose any directory structure you’re comfortable with. Hopefully, that guide will help you to get started faster or, at least, be your Kotlin trigger? Packages Also, I tried to be concise by favoring commented snippets over long explanations.

While not a replacement to the sources cited above (despite being highly inspired by them), I wrote that guide for Java Developers trying to focus on differences and new idioms. Back in 2017, it doesn’t take long for it to skyrocket after Google announced Kotlin as an official language for Android.Īlthough being concise and easy to get started with, on-boarding developers to Kotlin might require some time but Java Developers could take a lot of shortcuts navigating their way through the official documentation or through the highly recommended “ Kotlin In Action”. Unless you lived in a cave for the last two years, you probably noticed that Kotlin is here and going to stay for a long time.

Kotlin range operator