敏捷软件开发（上篇）

        if(NUMBER_IN_DECK[card.getValue()] == countOf(card))
            throw new IllegalStateException("Cannot add more cards of value " +
                                                 card.getValue());

        cards.add(card);
    }

    public Card top()
    {
        if(isEmpty())
            throw new IllegalStateException("Cannot call top on an empty deck");

        return (Card) cards.get(0);
    }

    …

    private int countOf(Card card)
    {
        int result = 0;

        for(Iterator i = cards.iterator(); i.hasNext(); )
        {
            Card each = (Card) i.next();
            if(each.getValue() == card.getValue())
                result++;
        }

        return result;
    }
}

public class Hand
{
    …

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