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"