When converting java to groovy it is quite often to get new Runnable() { public void run() { } } flagged in the editor with "Cannot instantiate interface" - note that it wworks only for interfaces, not for abstract classes! At this point we could provide an intelligent quick fix that would convert one-method interface instantiation to closure, and many methods to map as MyInterface: MyInterface i = [m1: {}, .. mn : {}] as MyInterface Note that in case of overloading we'd have to put the methods with List arguments and dispatch at runtime.