Java Game Programming For Dummies - W. Holder, D. Bell

Designing the game

The first step in designing an object-oriented program (Remember: Java is an object-oriented programming language) is to look at the objects being modeled by the program. Figure 6-1 shows the objects in a real game of Blackjack.

li t

.,tT-lWIT.: IIr

96 Part II: Up to Speed

After you identify the objects your game needs to model, you need to organize the objects according to their relationships and functions in the game. Although programming challenges usually have more than one solution, the elements typically suggest certain logical relationships that, in turn, suggest the most elegant way to program them. The Blackjack game presented in this chapter organizes the elements of Blackjack, as shown in Figure 6-2.

relationships.

As Figure 6-2 shows, the Blackjack Applet provides the playing surface and contains an array of player objects, a dealer hand object, a deck object, and a user interface. The deck and dealer hand objects each contain an array of card objects. Each player object contains a player hand object and a bankroll. The player hand contains an array of card objects and a bet. The user interface is a panel component that contains the button objects for the various options available to the player. The fact that the object relationships for Blackjack look similar to the layout of the real-world "objects" is no coincidence: The game design is derived from the real-world objects.

Creating a Reusable Deck a f Cards

A deck of cards is a common element to all card games (bet you didn't know that), and many of the techniques presented in this section can be applied tc any card game you want to program. You can even create specialized decks (for example, Pinochle or Poker with the Joker added) with minor changes here and there, as we explain a bit later in this chapter.

One of the powerful aspects of object-oriented programming is how it facilitates reusing code. This section shows how to create a reusable Deck class that you can use in any card game that uses a standard deck. This section also presents the Ca rd objects that the Deck class shuffles and deals.

98 Part I1: Up to Speed

(continued)

// Deals the top, card from the deck

public Card deal () throws NoSuchElementException I return deal(O);

1

1/ Deals a card from the deck. <pos> is relative to the top of the deck (0 = top, 1 = second from top, etc.)

public synchronized Card deal (int pos) throws NoSuchElementException

Card c = peek(pos);

if (pos > 0) //deal card from middle of deck System.arraycopy(cards, top - pos,

cards, top - pos - 1, pos);',

top--; return c;

//Returns the top card from the deck without dealing it public Card peek () throws NoSuchElementException I

return peek(0);

//Returns a card from the deck without dealing it.

//<pos> is relative to the top of the deck (0 = top)

`public synchronized Card peek -(int pos)

throws NoSuchElementException

if (POs < 0)

throw new NoSuchElementException();

try I return cards[top - (pos + 1)1; l catch (lndexOutOfBoundsException e) { throw new NoSuchElementException();

l

// end class Deck

The algorithm used in Deck. shuffle( ) works by swapping each card in the deck with another randomly selected card. This swapping randomizes the deck after a single pass through the deck and is much simpler than simulating a real shuffle.

100 Part II: Up to Speed

(continued)

public static final int

JOKER = 0, ACE = 1, TWO = 2, THREE = 3, FOUR = A,

FIVE = 5, SIX = 6, SEVEN = 7, EIGHT = 8, NINE _ 9,"

TEN = 10, JACK = 11, QUEEN = 12, KING = 13;

private static final String[] suitNames =

I Club , Diamond , Heart , Spade I;

private static final String[] rankNames =

I Joker , Ace , Two , Three , Four , Five

Six , Seven , Eight , Nine , Ten , Jack ,

Queen , King };

public final int getRank () ( return rank; I public final int getSuit () ( return suit; I public Card (int rank, int suit) I

if ((this.rank = rank) != JOKER) this.suit = suit;

I

public final String getSuitName ()

return rank == JOKER ? : suitNames[suit];

public final String getPluralSuitName () (

return rank == JOKER ? : suitNames[suit] + s-;

public final String getRankName ()

I return rankNames[rank];

public final String getPluralRankName ()

return rankNames[rank] + (rank == SIX ? es : s

public' final boolean isFace () return rank >= JACK;

I

102 Part I1: Up to Speed

(continued)

public String toString ()

StringBuffer buf = new StringBuffer(rankNames[rankl); if (rank != JOKER)

buf.append( of ).append(getPluralSuitName(-))-; return buf.toString();

public boolean equals (Object obj) { if (obj instanceof Card) f

Card c = (Card)obj;

return crank == rank && c.suit == suit;

1

return false;

public int hashCode () t

return (rank << 2) + suit;,

)

end, class Card

The Ca rd class supports Jokers even though Blackjack does not use a Joker. Ca rd is a general-purpose class useful for all kinds of games, including those that use a Joker.

Converting cards to strings

Most computer games use an image of a card to represent a card on screen, but sometimes cards need to be displayed as text. For example, if you are trying to develop and debug a game, you may want the cards to appear as text so that you can work out the process of the game before creating the images for the cards.

To convert cards to strings, override 0 b j e c t. t o S t r i n g ( ) so that it implicitly converts an object to a string when using the + string concatenation operator. A Ca rd object has methods for returning the plural and singular names of its suit and rank. C a r d uses these methods in t o S t r i n g ( ) to construct and return the name of the card.

For example, the following code displays The card is an Ace of Spades:

Card c = new Card(Card.ACE, Card.SPADE);

Part II: Up to Speed

10 4

Four rows of 14 card images - one row for each suit - combine to form the composite image. You call the static method i n i t G r a p h i c s ( ) to load the combined image. i n i t G r a p h i c s ( ) uses the Medi aTracker class discussed i n Chapter 5 to load the cardsImage image. i n i t G r a p h i c s ( ) calculates the width (ca rdWi dth) of an individual card by dividing the composite image's width by 14 and the height (c a rd H e i g h t) by dividing the composite's height by 4.

To draw a single card rather than the entire c a rd s I ma g e graphic, you need to define a clipping region to restrict where the graphics context draws pixels. To understand how a clipping region works, imagine that the graphics context is a piece of paper. To create a clipping region take another piece of paper the same size, cut a rectangular hole in it, and position it over the first piece of paper. Now when you draw on the graphics context, you can only draw within the clipping region. To draw a card from the c a r d s I m a g e graphic, you make the clipping region the size of a single card, then position c a r d s I ma g e to line up the desired card with the clipping region and call

d r a w I m a g e ( ) to draw the card. Figure 6-4 shows what this clipping image looks like if c a r d s I m a g e is a third piece of paper and you place it between the other two sheets of paper.

The draw( ) and drawCardBack( ) methods use card Wi dth and

c a r d H e i g h t to calculate the x,y pixel coordinates of the upper-left corner of the image to extract from c a r d s I ma ge. These methods pass the x,y pixel coordinates to d o D r a w ( ), which uses them as the offsets for positioning

c a rd s I ma g e so that the card to be drawn is in the correct place relative to the clipping region. d o D r a w ( ) sets the clipping region and draws the card using the following code:

Graphics gcopy = g.create();

gcopy.clipRect(x, y, cardWidth, cardHeight); gcopy.drawImage(cardsImage, x - xoff, y - yoff, null); gcopy.dispose();