I have a third party Java library which an object with interface like this:
public interface Handler<C> { void call(C context) throws Exception; } How can I concisely implement it in Kotlin similar to Java anonymous class like this:
Handler<MyContext> handler = new Handler<MyContext> { @Override public void call(MyContext context) throws Exception { System.out.println("Hello world"); } } handler.call(myContext) // Prints "Hello world" Assuming the interface has only a single method you can make use of SAM.
val handler = Handler<String> { println("Hello: $it") } Since version 1.4 Kotlin supports SAM for interfaces defined in Kotlin. That requires prefixing the interface keyword with fun
fun interface Handler<C> { fun call(context: C); } If you have a method that accepts a handler then you can even omit type arguments:
fun acceptHandler(handler:Handler<String>){} acceptHandler(Handler { println("Hello: $it") }) acceptHandler({ println("Hello: $it") }) acceptHandler { println("Hello: $it") } If the interface has more than one method the syntax is a bit more verbose:
val handler = object: Handler2<String> { override fun call(context: String?) { println("Call: $context") } override fun run(context: String?) { println("Run: $context") } } 
acceptHandler { println("Hello: $it")} would also work in most cases
fun interface.
I had a case where I did not want to create a var for it but do it inline. The way I achieved it is
funA(object: InterfaceListener { override fun OnMethod1() {} override fun OnMethod2() {} }) 
val obj = object : MyInterface { override fun function1(arg:Int) { ... } override fun function12(arg:Int,arg:Int) { ... } } 
As of Kotlin 1.4 you can declare a functional interface:
fun interface Handler<C> { fun call(context: C); } and then you can create one concisely:
val handler = Handler<String> { println("Handling $it") } The simplest answer probably is the Kotlin's lambda:
val handler = Handler<MyContext> { println("Hello world") } handler.call(myContext) // Prints "Hello world"