kotlin-interop

In Java I have the possibility to "implement" annotations. Sample Java annotation: @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) public @interface JavaClassAnno { String[] value(); } Sample Java "implementation": class MyAnnotationLiteral extends AnnotationLiteral<JavaClassAnno> implements JavaClassAnno { // <--- works in Java private String value; public MyAnnotationLiteral(String value) { this.value = value; } @Override public String[] value() { return new String[] { value }; } } Trying to port that to Kotlin doesn't work as it says that the annotation is final and therefore

If I have a Kotlin function fun f(cb: (Int) -> Unit) and I want to call f from Java, I have to do it like: f(i -> { dosomething(); return Unit.INSTANCE; }); which looks very ugly. Why can't I just write it like f(i -> dosomething()); , since Unit in Kotlin is equivalent to void in Java? Unit in Kotlin is mostly equivalent to void in Java, however only when the rules of the JVM allow it. Functional types in Kotlin are represented by interfaces like: public interface Function1<in P1, out R> : Function<R> { /** Invokes the function with the specified argument. */ public operator fun invoke(p1: P1

How to make a property in Kotlin that has a private getter (or just do not have it) but has a public setter? var status private get doesn't work with an error: Getter visibility must be the same as property visibility In my case, the reason is for Java interop: I want my Java code to be able to call setStatus but not getStatus . It's impossible at the moment in Kotlin to have a property with a setter that is more visible than the property. There's a language design issue in the issue tracker on this, feel free to watch/vote for it or share your use cases: https://youtrack.jetbrains.com/issue

How can I convert my Kotlin Array to a varargs Java String[] ? val angularRoutings = arrayOf<String>("/language", "/home") // this doesn't work web.ignoring().antMatchers(angularRoutings) How to pass an ArrayList to a varargs method parameter? You should use the " spread operator ", which looks like this: * The spread operator needs to be prefixed to the array argument: antMatchers(*angularRoutings) For further information, see the documentation : When we call a vararg -function, we can pass arguments one-by-one, e.g. asList(1, 2, 3) , or, if we already have an array and want to pass its