An invisible class too!

Our analysis of the classes required by our specification is sound as far as it goes, but it leaves something out. Deck and Hand are both what are called collection classes. They each collect a group of objects of another type. What then is this other type? Well decks of cards and hands of cards are both made up of cards, so our code will also require a Card class. It is not easy to tell what methods this card class will have to provide since none are explicitly visible, but we'll add an empty Card class to our module now, and add methods to it later as we discover they are necessary in working on our Deck and Hand classes: