i dont have the K&B book but basing from the code
i have the following doubtful explanation.Hope you dont mind.
1) for Letter A = you cannot assign class Bing to class Bang because
class Bing is a superclass. It will cause a runtime error.
2) for Letter B = the class Bing does not have a constructor that takes an int parameter.
3) for Letter C = its obviously correct.
4) for Letter D = it creates an anonymous class of type Bang and stores it to
a type of class Bing. It is perfectly legal because Bang is a subclass of class Bing.
cheers,
arnel