Why Diffrence of annomous Impl of Interface declared in between Java and Kotlin

[ronnin]

inteface with only one method

1. declared in Java, annomous impl can writtern in closure form, like fun call

2. declared in Kotlin, annomous impl should use " object:".
   eg:

   public interface JMathJob {
   Integer plus(Integer left, Integer right);
   }
   interface KMathJob {
   fun plus(left: Int, right: Int): Int
   }
   val jjob = JMathJob { left, right → left + right } // valid
   val kjob = KMathJob { left, right → left + right } // invalid

why ?

[Dittert]

This is called SAM conversion and Kotlin only supports this for Java interfaces and not for Kotlin code. The documentation says:

Also note that this feature works only for Java interop; since Kotlin has proper function types, automatic conversion of functions into implementations of Kotlin interfaces is unnecessary and therefore unsupported.

If you want to dig deeper into this, here are a two past discussions of this topic:

Kotlin SAM traits as lambda functions

around M5-M6 Kotlin gained support for calling java SAM's (Single Abstract Methods, think Runnable Interface) with a lambda function.  This allowed you to do //kotlin code SwingUtilities.invokeLater{   //some code here } //is the same as this code SwingUtilities.invokeLater(object : Runnable {   override fun run() {   //some code here   } }   However if the SAM is a kotlin Trait, this does not work for some reason... are their plans to allow Kotlin SAM Traits to be called like Lambda'…

Kotlin and SAM interface with two parameters

I'm trying to get a SAM with two parameters to work with a Kotlin closure. The best I could do is this: // Javapublic interface Two {   Integer f(Integer i, String s);} // Kotlinfun f2(two: Two) {} fun test() {   f2 ( Two { i, s -> 42 } )} I expected to be able to write: f2 { i, s -> 42 } Why do I need to explicitly coerce this expression to `Two`?

[fvasco]

Java and Kotlin are 99% interoperable.

See https://youtrack.jetbrains.com/issue/KT-7770