java - Why is this val, not a val? -

this 1 seems dependant on interaction between java , kotlin, first java class:

public class myjavaclass {     private runnable q;      public void setrunnable(final runnable listener) {         q = listener;     }      public boolean testcontains(final runnable listener) {         return q == listener;     } } 

now kotlin tests:

class javainteractiontests {      @test     fun `anonymous`() {         val abc = object : runnable {             override fun run() {              }         }          val x = myjavaclass()          x.setrunnable(abc)         asserttrue(x.testcontains(abc))     }      @test     fun `lambda`() {         val abc = runnable { }          val x = myjavaclass()          x.setrunnable(abc)         asserttrue(x.testcontains(abc))     }      @test     fun `function`() {         val abc: () -> unit = {}          val x = myjavaclass()          x.setrunnable(abc)         asserttrue(x.testcontains(abc))     }  } 

the last test fails, appear val isn't val.

bug or explainable, expected behaviour?

note, if java class defined in kotlin so, last test not compile:

class myktclass {     private var q: runnable? = null      fun setrunnable(listener: runnable) {         q = listener     }      fun testcontains(listener: runnable): boolean {         return q === listener     } } 

(i noticed when registering callback java class, going remove later , failed removed. callback defined in 3rd test style)

the reason that, each time when call java function accepts runnable , pass kotlin function () -> unit it, runnable implicitly created wraps function.

and when twice (x.setrunnable(abc) , x.testcontains(abc)), these 2 different runnables not equal each other, hence failure.

this how sam conversion works in kotlin. basically, these calls equivalent

val abc: () -> unit = {}  val x = myjavaclass()  x.setrunnable(runnable(abc)) // 1 runnable asserttrue(x.testcontains(runnable(abc))) // runnable 

also, kotlin not support sam conversions functions defined in kotlin, that's why test not compile when re-write class in kotlin. reasoning kotlin has functional types, , should used instead of sam interfaces. so, sam conversion rather mean of java interop complete language feature.