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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