Kotlin - no_image

JvmOverloads annotation

Instructs the Kotlin compiler to generate overloads for this function that substitute default parameter values.

If a method has N parameters and M of which have default values, M overloads are generated: the first one takes N-1 parameters (all but the last one that takes a default value), the second takes N-2 parameters, and so on.

Functions with parameters having a default value must use @JvmOverloads. Without this annotation it is impossible to invoke the Kotlin function using any default values from Java.

When using @JvmOverloads, inspect the generated methods to ensure they each make sense. If they do not, perform one or both of the following refactorings until satisfied:

• Change the parameter order to prefer those with defaults being towards the end.
• Move the defaults into manual function overloads.

Incorrect: No @JvmOverloads

class Greeting {
    fun sayHello(prefix: String = "Mr.", name: String) {
        println("Hello, $prefix $name")
    }
}

public class JavaClass {
    public static void main(String... args) {
        Greeting greeting = new Greeting();
        greeting.sayHello("Mr.", "Bob");
    }
}

Correct: @JvmOverloads annotation.

class Greeting {
    @JvmOverloads
    fun sayHello(prefix: String = "Mr.", name: String) {
        println("Hello, $prefix $name")
    }
}

public class JavaClass {
    public static void main(String... args) {
        Greeting greeting = new Greeting();
        greeting.sayHello("Bob");
    }
}

Links

JvmOverloads
Kotlin-Java interop guide

Further reading

Misconception about Kotlin @JvmOverloads for Android View Creation
@JvmOverloads for Android Views

credit goes to @swayangjit