J2ME Canvas Example

A J2ME Game Canvas Example

This example illustrates how to create a game using GameCanvas class. In this example we are extending GameCanvas class to draw the circle and rotate the circle continuously. The GameCanvas class has following methods:

flushGraphics():- This is the void type method, it flushes to display on the off-screen buffer.
flushGraphics(int x, int y, int width, int height):- This is the void type method, it flushes to display of specified region on the off-screen buffer.
getGraphics():- This is used to get the graphics objects.
getKeyStates():- This is the integer type variable, it is used to find the states of the key.
paint(Graphics g):- This is also the void type method, it is used to paint the canvas.

Other commands, input event, etc methods inherited from Canvas class. The Canvas class has following methods:

getGameAction(int keyCode)
getHeight()
getKeyCode(int gameAction)
getKeyName(int keyCode)
getWidth()
hasPointerEvents()
hasPointerMotionEvents()
hasRepeatEvents()
hideNotify()
isDoubleBuffered()
keyPressed(int keyCode)
keyReleased(int keyCode)
keyRepeated(int keyCode)
paint(Graphics g)
pointerDragged(int x, int y)
pointerPressed(int x, int y)
pointerReleased(int x, int y)
repaint()
repaint(int x, int y, int width, int height)
serviceRepaints()
showNotify()

Source Code of CanvasGame.java


import javax.microedition.lcdui.*;

import javax.microedition.lcdui.game.*;

import javax.microedition.midlet.*;



public class CanvasGame extends MIDlet{



  private Command back;

  private Display display;

  final SweepGame game = new SweepGame();



  public void startApp() {

    back = new Command("Back", Command.BACK, 0);

    game.start();

    game.addCommand(back);

    game.setCommandListener(new CommandListener(){

      public void commandAction(Command c, Displayable s) {

        game.stop();

        notifyDestroyed();

      }

    });

    display = Display.getDisplay(this);

    display.setCurrent(game);

  }



  public void pauseApp() {}



  public void destroyApp(boolean unconditional) {}

}



class SweepGame extends GameCanvas implements Runnable {

  private boolean move;

  private int radius;

  private int diameter;

  private int interval;



  public SweepGame() {

    super(true);

    radius = 0;

    diameter = 10;

    interval = 0;

  }

  public void start() {

    move = true;

    Thread t = new Thread(this);

    t.start();

  }

  public void stop() {

    move = false;

  }

  public void render(Graphics g) {

    int width = getWidth();

    int height = getHeight();

    g.setColor(183,251,121);

    g.fillRect(0, 0, width - 1, height - 1);

    int x = diameter;

    int y = diameter;

    int w = width - diameter * 2;

    int h = height - diameter * 2;

    for (int i = 0; i < 17; i=i+2) {

      g.setColor(((17 - i) * 15 - 7),20,((17 - i) * 15 - 7));

      g.fillArc(x, y, w, h, radius + i * 10, 10);

      g.fillArc(x, y, w, h, (radius + 180) % 360 + i * 10, 10);

    }

  }

  public void run() {

    Graphics g = getGraphics();

    while (move) {

      radius = (radius + 1) % 360;

      render(g);

      flushGraphics();

      try {

        Thread.sleep(interval);

      }

      catch (InterruptedException ie) {}

    }

  }

}

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