Java

public class Card {
    private final int rank;
    private final int suit;

    // Kinds of suits
    public final static int DIAMONDS = 1;
    public final static int CLUBS    = 2;
    
    // Kinds of ranks
    public final static int ACE   = 1;
    public final static int DEUCE = 2;
     
    public Card(int rank, int suit) {
        assert isValidRank(rank);
        assert isValidSuit(suit);
        this.rank = rank;
        this.suit = suit;
    }

    public int getSuit() {
        return suit;
    }

    public int getRank() {
        return rank;
    }

    public static boolean isValidRank(int rank) {
        return ACE <= rank && rank <= KING;
    }

    public static boolean isValidSuit(int suit) {
        return DIAMONDS <= suit && suit <= SPADES;
    }

    public static String rankToString(int rank) {
        switch (rank) {
        case ACE:
            return "Ace";
        case DEUCE:
            return "Deuce";
                default:
                return null;
        }    
    }
    
    public static String suitToString(int suit) {
        switch (suit) {
        case DIAMONDS:
            return "Diamonds";
        case CLUBS:
            return "Clubs";
                default:
            return null;
        }    
    }

    public static void main(String[] args) {
    	    	// use assert statements
        assert rankToString(ACE) == "Ace";
        assert rankToString(DEUCE) == "Deuce";
        
    }
}