從科特林創建的Java SAM界面給人ClassCastException異常

Question

我有一個Java方法：

addHandler(HttpServiceHandler handler) 

HttpServiceHandler是

interface HttpServiceHandler extends Consumer<HttpHandlerContext> 

的一點是要避免在項目Consumer<HttpHandlerContext>複製粘貼，所以它是一種一個類型別名。

在Java代碼中，這個工程的所有權利：現在

addHandler({ context -> context.blah(); }) 

，在科特林，我有這種方法生成的處理程序：

private companion object { 
    fun newHandler(notimportant: Long): HttpServiceHandler { 
     return HttpServiceHandler { context -> context.blah() } 
    } 
} 

HttpServiceHandler {}是很重要的，它並不如編譯我沒有爲lambda指定HttpServiceHandler。

這編譯：

addHandler(newHandler(1L)) 

但在運行時，會拋出：

java.lang.ClassCastException: blah.BlahTest$Companion$newHandler$1 cannot be cast to kotlin.jvm.functions.Function1 

at blah.BlahTest.test(BlahTest.kt:42) 
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) 
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 
at java.lang.reflect.Method.invoke(Method.java:498) 
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) 
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) 
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) 
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) 
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) 
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) 
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) 
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) 
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) 
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) 
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) 
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) 
at org.junit.runners.ParentRunner.run(ParentRunner.java:363) 
at org.junit.runner.JUnitCore.run(JUnitCore.java:137) 
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68) 
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51) 
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242) 
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70) 

而且我想不通爲什麼。請幫助？

更新：，如果我把它寫這樣的類轉換異常消失：

addHandler(
    object : HttpServiceHandler { 
     override fun accept(c: HttpHandlerContext) { 
      c.complete() 
     } 
    } 
) 

但仍然拋出的時候這樣寫的除外：

fun newHandler(blah: Long): HttpServiceHandler { 
    return object : HttpServiceHandler { 
     override fun accept(c: HttpHandlerContext) { 
      c.complete() 
     } 
    } 
} 

addHandler(newHandler(1L)) 

而且我也沒辦法爲什麼。

更新2：測試代碼在https://github.com/wilem82/testcases/tree/master/kotlinsam1。不幸的是，這並不能重現問題。

Answer 1

誤差已經精確地說：

java.lang.ClassCastException：blah.BlahTest $伴侶$ newHandler $ 1不能被轉換爲kotlin.jvm.functions。功能1

您嘗試投下Consumer<HttpHandlerContext>到Function1在addHandler法或其他地方，例如：

fun addHandler(handler: Consumer<HttpHandlerContext>) { 
    val it: Function1<*, *> = handler as Function1<*, *> 
    //      ^
    // ClassCastException was thrown since it is not a Function1 
} 

你應該使用方法參照表達在Java /函數參考表達科特林轉換一個SAM接口到另一個SAM接口，例如：

fun addHandler(handler: Consumer<HttpHandlerContext>) { 
    val it: Function1<HttpHandlerContext, Unit> = handler::accept 
    //  using function reference expression here  ---^ 
    //... 
} 

IF你打電話JAV在科特林方法addHandler，你不必創建這樣一個橋法newHandler，你可以使用拉姆達叫它科特林，例如：

addHandler{context-> 
    context.blah() 
    // additional works ... 
}