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

106 Part 11: Up to Speed

In addition, you can extend the Deck class to play Poker with a joker in the deck or to play games such as Pinochle that use a nonstandard deck of cards. You override p a c k S i z e ( ) and r e s h u f f 1 e ( ) to initialize the custom deck. A Pinochle deck has 48 cards - two of each suit of the ranks nine through ace. You implement a Pinochle deck like this:

public class PinochleDeck extends Deck I

public PinochleDeck () ( super(); f

public PinochleDeck (int packs) ( super(packs); I

public int packSize (;) ( return 48; }

public synchronized void reshuffle () ( top = 0:

for tint packs = this.packs * 2; --packs >= 0; )

for (int suit = Card.C'LUB; suit <= Card.SPADE; suit++)

(

for (Int rank = Card.NINE; rank <= Card.KING; rank++) cards[top++] = new Card(rank, suit);

cards[top++] = new Card(Card.ACE, suit):

shuffle():

1

l II end class PinochleDeck

Creating a User Interface with Components

You create a user interface in Java from AWT components. Component is an abstract class in the j ava. awt package that embodies all the common functions of user interface elements. You build your interface from the subclasses of Component: Button, Canvas, Checkbox, Choi ce, Label, Li s - ScrolIbar,TextArea,and TextField.

Using buttons

Buttons are a common interface element. You use buttons to represent an action the user can perform. Unlike menus, which also represent available actions, a button is

W Visible, so the user doesn't have to look through menus to determine what actions are available.

-Convenient, because it requires a single mouse click to perform the associated action.

108 Part II: Up to Speed

Having your game respond to buttons

Button converts a mouse click into an ACT I ON-EVENT. You override Component. a c t i on() in the parent container in order to handle action events. You identify the button that generated the event in a c t i o n ( ) by comparing the Event. t a r g e t field to the Button objector, alternately, by comparing the field to the button label string.

Here is an example of an applet creating and responding to a button:

i mport java awt.*;

public class ColoredApplet extends java.applet.Applet I private Button red = new Button( Red );

private Button blue = new Button( Blue ); public void init () i

add( red); add( blue); l ayout();

public boolean action (Event evt. Object arg) I i f (evt.target == red)

setBackground(Color.red); else if ( Blue equals(arg)) setBackground(Color.blue):

repaint(); return true;

I // end class ColoredApplet

Notice that the a ct i on ( ) method in Col oredApp I et uses the evt . to rget field to find the red button and uses the a rg parameter to identify the bl ue button. We include both techniques in the example just to show both ways of checking. However, the evt. t a r g e t way is faster, because comparing object references is less work than comparing strings.

Reading and displa ying text

At some point, most programs need to display text or collect information entered by the user. Java 1.0 provides three components for displaying text: Text Fi el d, TextArea, and Label. The Blackjack applet uses labels to display each player's name and current bankroll. Text Fi el d and TextArea also accept text typed by the user. Text Fi el d displays and accepts a single line of text; TextArea creates a scrollable, editable text area that displays multiple lines. This section shows how to use each of these components.

Chapter 6: Blackjack

The following example uses a Label, Text Field, and TextArea:

i mport java.awt.*;

public class ListEntry extends java.applet.Applet I

static final String newline =

public void init () I list.setEditable(false): add( Iist);

add(new Label( Name: . Label.RIGNT)); add(entry);

public boolean action (Event evt, Object arg) if (evt.target == entry) I

list.appendText(entry.getText() + newline): entry.selectAll();

return true;

return false;

I ll end class ListEntry

creates a Text Area that holds five lines of approximately 20 characters each and a that holds a single line of approximately

20 characters. The AWT calls L i s t E n t ry . action() when the user presses the Enter or Return key in the e n t ry text field. a c t i o n ( ) appends the

e n t ry text to the 1 i s t text area and selects the text in e n t ry so that the next text that the user types replaces the current text. Figure 6-6 shows the program running.

App

tFp.1ty

George Washington

Thomas Jefferson

RRroham Lincoln

Teddy Roosevelt

Ronald Reaoen

Name: Ronald Reagan

Ao Ut strted

112 Part II: Up to Speed

The System.getProperty( line.separator ) call in the preceding

example gets the system-dependent character string used to separate lines text. You would think that operating systems would standardize on something as simple and basic as a line separator, but they don't. Under UNIXbased operating systems, the separator is a linefeed character (\ n); under Mac OS, the separator is a carriage return character (\ r); and under DOS and Windows operating systems, the separator is a carriage return follo w by a linefeed (\

Using C a n v a s to create new components

A C a n v a s component is a way to create your own component - it provides all the hooks to collect user events and draw itself, but the default canvas is basically a blank slate. You can use C a n v a s to create your game's playfield, displays, and just about anything else that you want to display a certain way.

Customizing your game's appearance With I m a g e B u t t o n

The AWT components are functional but not particularly colorful. You can design your own custom components by subclassing the C a n v a s component. The simplest and probably the most useful component to customize is Button. The following I mageButton class uses two images-the pressed and unpressed button images - rather than the standard button with a text label:

i mport java.awt.*;

public class ImageButton extends Canvas implements Runnable I

public ImageButton (Image up, Image down)

tg = Thread.currentThread().getThreadGroup(); i mg[0] = up;

img[1] = down;

)

public synchronized Dimension minimumSize () int x = Math.max(img[0].getWidth(null),

img[1].getWidth(null));

int y = Math.max(img[Ol.getHeight(null),

img[1l.getHeight(null)):

return new Dimension(x < 0 ? 10 : x; y < 0 ? 10 : y).;

Chapter 6: Blackjack 113

public Dimension preferredSize () I return minimumSize();

public void paint (Graphics g) t if (img[imgndx] != null)

g.drawImage(img[imgndx1, 0, 0, this);

public void update (Graphics g) 1 paint(g);

I

public synchronized void run () i mgndx = l;

repaint();

Component p = getParent{); i f (p != null)

p.postEvent{new Event(this, Event.ACTION EVENT, i mg[01));

try I Thread.sleep(200); } // press for 1/5 second catch (InterruptedException e) I}

i mgndx = 0; repaint();

public synchronized boolean mouseDown (Event evt,

i nt x, int y) I

(new Thread(tg, this)).start(); return true;

1

/f end class ImageButton

The following are the key points for implementing ImageButton:

V ImageButton overrides Component. preferredSize() and Component. mini mumSi ze ( ) in order to have the button automatically size itself to the size of the largest image.

V mo u s e D own ( ) spawns a thread to animate the button press so that it doesn't perform the animation in the AWT Interface thread. (CD Chapter 2 explains what the AWT Interface thread is and how to spawn threads from and other event handlers.)

vmouseDown( ) and run( ) are synchroni zed to prevent the animation from being interrupted. Synchronization prevents mouse clicks from being processed faster than the animation rate.