Scala反射，使用asInstanceOf强制转换类型

Question

I have

trait T
class C extends T

compiled to .class files. Run scala with -cp <...> to have type T available. Then load class C using reflection:

val loader = ScalaClassLoader fromURLs (/* List[URL] */)
val anyC = loader.tryToInitializeClass("C") getOrElse (/* throw something */)
val classC = anyC.asInstanceOf[Class[T]]

How can I cast a classC.newInstance into type T like

val objC = classC.newInstance.asInstanceOf[T] 
// yields java.lang.ClassCastException: C cannot be cast to T

Answer 1

You must be loading class C from a different classloader than the one T is being loaded from.

You've put both T and C on the REPLs classpath, so one option would be to load C via the system classloader. Sample REPL session,

scala> val loader = scala.tools.nsc.util.ScalaClassLoader.getSystemLoader
loader: scala.tools.nsc.util.ScalaClassLoader =
  scala.tools.nsc.util.ScalaClassLoader$$anon$1@985d2e0

scala> val anyC = loader.tryToInitializeClass("C") getOrElse (sys.error("Boom"))
anyC: Class[Nothing] = class C

scala> val classC = anyC.asInstanceOf[Class[T]]
classC: Class[T] = class C

Nb. this isn't really a Scala-specific question any longer.