Help displaying an image using the canvas!!!!!!!!

Question

Hey guys
I don't know whether I am not grasping some concepts well.I have been going mad trying to get the code working
Here is the code
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.io.*;
* @author Administrator
* @version
public class MyMIDlet extends javax.microedition.midlet.MIDlet implements CommandListener{
private Display display;
private MyCanvas canvas;
private Command exitcommand = new Command("Exit",Command.SCREEN,1);
private Image source;
public MyMIDlet() {
protected void startApp() throws MIDletStateChangeException{
if (display == null){
initMIDlet();
protected void pauseApp() {
protected void destroyApp(boolean unconditional)throws MIDletStateChangeException {
exitMIDlet();
public void commandAction(Command c, Displayable d) {
if (c == exitcommand){
exitMIDlet();
protected void initMIDlet() {
display = Display.getDisplay(this);
canvas = new MyCanvas(this);
System.err.println("Canvas instiated succesfully");
canvas.addCommand(exitcommand);
canvas.setCommandListener(this);
display.setCurrent(canvas);
public void exitMIDlet() {
notifyDestroyed();
import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;
import java.io.*;
public class MyCanvas extends Canvas implements Runnable {
private MIDlet midlet;
private Image offscreen;
private Image currentimage;
private Graphics g;
//MID profile application
/** Creates a new instance of MyCanvas */
public MyCanvas(MIDlet midlet) {
this.midlet = midlet;
try{
currentimage = Image.createImage("/bird0.png");
}catch(IOException e){
System.err.println(e.getMessage());
if (currentimage!= null){
System.err.println("Image create successfully");
}else{
System.err.println("Image not created");
try{
Thread t = new Thread(this);
t.start();
}catch(Execption e){}
protected void paint(Graphics g){
Graphics saved = g;
int x = getWidth();
int y = getHeight();
g.setColor(255,255,255);
g.drawImage(currentimage,x,y,g.TOP|g.VCENTER);
public void run() {
repaint();
I know for a fact that the Canvas class 's paint method is called by the system and not the application. This poses a problem for me because I am not sure how to pass the image to the piant method, so that it can be painted.
When I run the program(using J2ME wtk04), this is the outcome.
Image created succesfully
Canvas instiatiated successfully
null
Here are my questions
1) when is the paint method precisely called by the system?after a reference to the canvas class is created?
2) is it wise to create the image when instiating the canvas class?( initially created the image using a separate thread)-when sould the image be created?
3)how to let the application know when to use the image when painting the display area?
I am just trying the logistics here. It is very crucial to me to understand the bolts of this as the core f my project fouses on the man machine interface development.(For the project, the cilent application is quering for the map using HTTP)
I use a png file of size 161 bytes. Is that too big for testing purposes.
I would all the help that I can get. thanks in advance

Answer 1

1) when is the paint method precisely called by the system?after a reference to the canvas class is created?
After the canvas is set as the current display, and after that, after the repaint() is called.
2) is it wise to create the image when instiating the canvas class?( initially created the image using a separate thread)-when sould the image be created?
It's better to create the image in the very begining of the program e.g. in the midlet initialization. You can call the created image as often as you like later on
3)how to let the application know when to use the image when painting the display area?
you have to tell it :))
you can use if-then, switch, or anything else
and you can use clipping too