5.4: Dealing Cards

At this point we can create a Deck and start dealing cards. Here’s a simple example that deals five cards to a hand, and deals the rest into a draw pile:

Deck deck = new Deck("Deck");
deck.shuffle();

Hand hand = new Hand("Hand");
deck.deal(hand, 5);
hand.display();

Hand drawPile = new Hand("Draw Pile");
deck.dealAll(drawPile);
System.out.printf("Draw Pile has %d cards.\n",
                  drawPile.size());

CardCollection provides dealAll, which deals all of the remaining cards. Here’s the output of the previous example:

Hand:
5 of Diamonds
Ace of Hearts
6 of Clubs
6 of Diamonds
2 of Clubs

Draw Pile has 47 cards. 

Of course, if you run this example you will probably get a different hand, because the deck is shuffled randomly.

If you are a careful reader, you might notice something strange about this example. Take another look at the definition of deal:

public void deal(CardCollection that, int n) {
    for (int i = 0; i < n; i++) {
        Card card = popCard();
        that.addCard(card);
    }
}

Notice that the first parameter is supposed to be a CardCollection. But we invoked it like this:

Hand hand = new Hand("Hand");
deck.deal(hand, 5); 

The argument is a Hand, not a CardCollection. So why is this example legal? It’s because Hand is a subclass of CardCollection, so a Hand object is also considered to be a CardCollection object. If a method expects a CardCollection, you can give it a Hand, a Deck, or a CardCollection.

But it doesn’t work the other way around: not every CardCollection is a Hand, so if a method expects a Hand, you have to give it a Hand, not a CardCollection.

If it seems strange that an object can belong to more than one type, remember that this happens in real life, too. Every cat is also a mammal, and every mammal is also an animal. But not every animal is a mammal, and not every mammal is a cat.