Design Constraints

The wide range of screen sizes, keyboard layouts and processing power in cellphones makes developing generic java applications a tricky business. The compromises that must be made to ensure that the application runs on all platforms severely limits functionality and performance. Most games are therefore written specifically for a family of phones from a single manufacturer. Popular games may be rewritten to provide versions for a number of manufacturers. These issues notwithstanding, it was decided to design and implement a generic game, based on rolling a ball through a maze. The game was designated 'Tilt'

Tilt.java

This file contains the main application class Tilt and two alternative classes for controlling the display. Class SmsForm is used when support for SMS is detected, while class NoSmsForm is used when no SMS support is available. This technique results in considerable code duplication, when compared to just encapsulating all SMS related functions in a separate helper class, but has the advantage of placing all the high priority keyboard and SMS handling in a single class. This appears to improve the response time of the application when receiving SMSs, which proved to be a critical issue when the application was tested on a Siemens S55 phone.

public class Tilt extends MIDlet implements Runnable {
    public Display display;
    public Splash splash;
    private Thread th = null;
    public Wrapper sms;
    public boolean initialised = false;

    public void startApp() { /* ... */ }
    public void pauseApp() { /* ... */ }
    public void destroyApp(boolean unconditional) { /* ... */ }
    public void run() { /* ... */ }
    class Splash extends Canvas {
        public Splash() { /* ... */ }
        public void paint(Graphics g) { /* ... */ }
}
class Wrapper extends Form { /* ... */ }

class SmsForm extends Wrapper implements CommandListener, ConnectionListener, Runnable {
    private volatile byte rPtr = 0, wPtr = 0;
    private byte[][] in = new byte[8][];
    Tilt parent;
    private Thread th1 = null, th2 = null;
    private boolean terminate = false, saving = false;
    private Command startCommand;
    private Command optionsCommand;
    public Connection conn  = null;
    public Game gm;
    public Options op;
    public Level lv;
    public SendForm tx;
    public Form hg;
    public Save sa;
    public Receive rx;
    public byte[] sd = new byte[Board.X_MAX * Board.Y_MAX];
    public byte[] rd;
    private byte buf1[] = new byte[256];
    private byte buf2[] = new byte[256];
    private byte out[];
    private boolean changedInbox = false, changed = false;
    Image level, gamepad, editpad;

    SmsForm() { /* ... */ }
    public void initialise(Tilt p) { /* ... */ }
    public void reset(boolean reg) { /* ... */ }
    private void append2(Image img) { /* ... */ }
    public void commandAction(Command cmd, Displayable disp) { /* ... */ }
    void send(byte[] data, String receiver) { /* ... */ }
    private void registerListener() { /* ... */ }
    private void removeListener() { /* ... */ }
    public void receiveData(byte[] data) { /* ... */ }
    private void saveReceivedData(byte[] data) { /* ... */ }
    public void storeReceivedData(int l) { /* ... */ }
    private void showAlert(String str) { /* ... */ }
    public byte[] compress(byte[] in) { /* ... */ }
    public byte[] expand(byte[] in) { /* ... */ }
    public void run() { /* ... */ }
    class Options extends List { /* ... */ }
    class Level extends List { /* ... */ }
    class Save extends Form { /* ... */ }
    class SendForm extends Form { /* ... */ }
    class Receive extends Form { /* ... */ }
}

Game.java

This file contains the single class Game. When the class is instantiated, it creates an instance of the class Board and determines the size of the System font. It also implements its own thread by inheriting interface Runnable. This thread is created by class SmsForm after it has instantiated class Game.

class Game extends Canvas implements Runnable {
    public Wrapper parent;
    public Board bd;
    private volatile byte direction = 0;              // Last keypress direction
    private boolean terminateGame = false;
    private boolean loadGame = false;
    private boolean saveGame = false;
    public boolean gamePaused = true;      // Game Paused
    public boolean gameOver = false;        // Game Over
    public int score = 0;                   // Game Score
    private Font f;
    private int height;
    private int showScore = 0;
    private boolean clearScreen;
    public boolean editMode = false;
    private int colour;
    
    Game(Wrapper p) { /* ... */ }
    public void setLevel(int l) { /* ... */ }
    public int getLevel() { /* ... */ }
    public void setEditMode() { /* ... */ }
    public void setNewGame() { /* ... */ }
    public void updateScore(int s) { /* ... */ }
    public void saveGame() { /* ... */ }
    public void loadGame() { /* ... */ }
    public void copyLevel(int level) { /* ... */ }
    public void terminateGame() { /* ... */ }
    public void keyPressed(int keyCode) { /* ... */ }
    public void keyReleased(int keyCode) { /* ... */ }
    public void run() { /* ... */ }
    protected void paint(Graphics g) { /* ... */ }
}

Board.java

This file contains the class Board, which in itself contains two important subclasses (class Images & class Ball). Class board primarily manages display of the game board, including scrolling the viewing area within the game level as the ball moves. Class Images loads all the graphics required by the game, while class Ball controls ball movement including collision detection.

class Board {
             public Game parent;
             public Images im;
             private Ball bl;
             public Image sc;
             public Image icon[][];
             public int height, width, colours;
             public boolean colour;
             private boolean newLevel = false;
             public int xm, ym;
             public int level = 1;
             public int xp=0, yp=0, xv=0, yv=0;
             static int X_MAX = 15;
             static int Y_MAX = 15;
             static int Z_MAX = 6;
             private int i, j, k;
             private RecordStore rs;

             public byte b[][][] = { /* ... */ }


    Board(Game p) { /* ... */ }
    public void newLevel(int l) { /* ... */ }
    public void move(int d) { /* ... */ }
    public void saveInbox() { /* ... */ }
    public void loadInbox() { /* ... */ }
    public void saveGame() { /* ... */ }
    public void loadGame() { /* ... */ }
    public void copyLevel(int copyTo) { /* ... */ }
    public void paint(Graphics g) { /* ... */ }
    class Images { /* ... */ }
    class Ball { /* ... */ }
        Ball(Board p) { /* ... */ }
        public void newLevel() { /* ... */ }
        public int Sensor(int x, int y) { /* ... */ }
        public void move(int d) { /* ... */ }
}