/**
     * Returns a string representation of the card "<rank> of <suit>"
     */
    public String toString()
    {
        String result = "";

        switch(rank)
        {
        case 1: result += "ace"; break;
        case 11: result += "jack"; break;
        case 12: result += "queen"; break;
        case 13: result += "king"; break;
        default: result += rank; break;
        }

        result += " of ";

        switch(suit)
        {
        case DIAMONDS: result += "diamonds"; break;
        case SPADES: result += "spades"; break;
        case HEARTS: result += "hearts"; break;
        case CLUBS: result += "clubs"; break;
        default: result += "invalid suit"; break;
        }

        return result;
    }