@JvmOverloads in Kotlin

10 Oct 2017

@JvmStatic and @JvmField are well-known annotations that can be used in Kotlin files to expose companion object methods and constants. But the other day I had an “oh wow” moment with @JvmOverloads so now it has joined the pantheon of great JVM annotations provied by Kotlin. Consider this method in a network utility written in Kotlin:

From a Kotlin file you can call this method in many ways:

But from Java you’re a little more restricted. Without the @JvmOverloads annotation from a Java file you would need to call the method with all three parameters: makeNetworkCall("www.mark.gg", 4, true). Adding @JvmOverloads generates two overloaded methods for you using the default values specified in the function declaration.

New programming languages like Swift and Kotlin can (naïvely) be evaluted solely on the merits of the language itself but a more accurate evaluation will look at the ecosystem: Xcode, Objective-C, Swift and Android Studio, Java, Kotlin. Annotations like @JvmOverloads make Kotlin a team player in an already established ecosystem giving it much more potential for disrupting and improving that ecosystem.