Create Instance of anonymous Controller and use its methods

Good morning dear board

There is a way in Java to make instances of anonymous classes:

Class<?> c = Class.forName("class name");
Method  method = c.getDeclaredMethod ("method name", parameterTypes)
method.invoke (objectToInvokeOn, params)

If I wished making new Instances of JavaFX Controllers I would just do this:

FXMLLoader loader = new FXMLLoader(getClass().getResource(
           "MyClass.fxml"));
MyClassCtrl ctrl = loader.getController();
Parent root = (Parent) loader.load();
ctrl.methodNameOfMyClassCtrl();

But now I have an example where I need to do instances of Controllers and use their methods, which aren't known while coding. They get known by runtime, depends on which Button was clicked by the user.

So what I need is a combination of the both techniques descriped above. Now I made following, but it won't work.

String methodName = "myMethod";
String className = "MyController";

FXMLLoader loader = new FXMLLoader(getClass().getResource( className + ".fxml" ));
Class c = Class.forName(className);
loader.setController(c);
Parent root = (Parent) loader.load();
Method m = c.getDeclaredMethod(methodName, null);
m.invoke(null, null);

I doubt, I'm the first trying something like this - so you guys are my last chance.

Thanks and best regards Enis