Scala: generate class from a string

Question

I want to dynamically create a Class from a String.

The String has the exact name of the Class (by the way is a Java class)

For example

val classString = "gui.MainFrame"

I create the class with

val mainClass: Class[_] = Class.forName(classString)

Scala founds the class, but if i want to use this class for example with

AppExecutor.executeNoBlock(classOf[mainClass])

Scala tells me that type mainClass cannot be found.

If i use it in that way

AppExecutor.executeNoBlock(mainClass.asInstanceOf)

it says that java.lang.Class cannot be cast to scala.runtime.Nothing$ So how can i use this class now?

mikołak · Accepted Answer · 2013-08-21 10:50:17Z

2

"You're holding it wrong."

classOf accepts a type parameter and returns a Class object. You can't pass a Class object as a type parameter, hence the error.

Also, you already have your Class object in mainClass. If you want to necessarily use classOf, you can do this:

val mainClass = classOf[gui.MainFrame]

instead. But otherwise you should stick to your previous approach, i.e.:

val mainClass = Class.forName(classString)

If the code you're trying to use is org.jemmy.fx.AppExecutor, you can just invoke it directly with mainClass:

AppExecutor.executeNoBlock(mainClass.asInstanceOf[Class[_ <: javafx.application.Application]])

Since the method apparently has a qualified type parameter (i.e. not a normal wildcard Class[_], or Class<?> in Java notation).

edited Aug 21, 2013 at 10:50

answered Aug 21, 2013 at 9:50

mikołak

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7 Comments

AKR Over a year ago

Yes you are right, i want to use the AppExecutor from Jemmy, and i know that i can call it directly with "mainClass", but the problem is, that the value of "mainClass" should not be the same every time. It should be variable, so that a user can enter another Class that is startet with AppExecutor. So i cannot use val mainClass = classOf[gui.MainFrame], because it would not be variable.

mikołak Over a year ago

@AKR : like I said, you can still use Class.forName(classString) if that's the case, the problem was in how you invoked executeNoBlock().

AKR Over a year ago

I tried it that way: "val mainClass = Class.forName(mainClassString)" and then "AppExecutor.executeNoBlock(mainClass)" but this leads to the error message "- overloaded method value executeNoBlock with alternatives: (x$1: Class[_ <: javafx.application.Application],x$2: <repeated...>[String])Unit <and> (x$1: Class[_ <: javafx.application.Application])Unit cannot be applied to (Class[?0(in value <local $anon>)])"

mikołak Over a year ago

@AKR. That's another story. Not sure if I got the cast correctly, but see my edit.

AKR Over a year ago

No problem. Thank you for your advice to accept the answer, i'm new to stackoverflow, so i haven't got all the features of this wonderful site now. ;)

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