You might have tried out the JavaFX Hello World example, from Oracle’s Getting Started with JavaFX guide, using Groovy.
You will then get the following exception:
Exception in thread "main" java.lang.RuntimeException: Error: class sun.reflect.NativeMethodAccessorImpl is not a subclass of javafx.application.Application
In order to fix this, change
launch(args);
to
launch(HelloWorld.class, args);
The example now runs fine with Groovy.