the following test fails:

import javax.swing.*

interface ISub extends Action {}

class Super extends AbstractAction {}
class Sub extends AbstractAction implements ISub {}

static String foo(Action x) { "super" }

static String foo(ISub x) { "sub" }

def result = [new Super(), new Sub()].collect { foo(it) }

assert ["super","sub"] == result // result is ["super","super"]

The special thing here is that Action is a Java interface. If you use
a Groovy interface instead, all works fine.