Can anybody help me with this code?

Question

I am a beginner to J2ME. The following is a small program I wrote just for test.
Theoretically, in my opinion, I shall see in the screen a number increase from 1 to 29999 rapidly after execute the code. But instead, it displays nothing but only displays 29999 after several seconds . Can some body point out what's wrong with this code? Thanks.
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class Test extends MIDlet{
int x=1;
String b="";
private Display display;
public Test() {
display = Display.getDisplay(this);
public void startApp() {
MyCanvas mc = new MyCanvas() ;
display.setCurrent(mc) ;
while(x<30000){
b=String.valueOf(x);
mc.repaint();
x++;
public void pauseApp() {
public void destroyApp(boolean unconditional) {
class MyCanvas extends Canvas{
public void paint(Graphics g){
g.drawString(b,10,10,0);

Answer 1

thanks, I have already got the answer. you are right, if repaint in a high speed the screen will show nothing. here is the code for it, thanks the expert of nokia forum.
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
//Counter
//Need to know when a number has been painted and need to wait a for a fraction of a sec before
//painting the next number. This wait also allows other events like "Exit" to be processed
//Use double buffering to avoid flicker
//Paint in a different thread to keep the UI responsive
public class MyMIDlet extends MIDlet{
int x=1;
String b="";
private Display display;
Thread t = null;
MyCanvas mc = null;
public MyMIDlet() {
display = Display.getDisplay(this);
public void startApp() {
mc = new MyCanvas();
t = new Thread(mc) ;
display.setCurrent(mc) ;
b=String.valueOf(x);
t.start();
public void callbackPaintDone(){
try{
//provides the delay between every repaint and also time to react to Exit
synchronized(this){
wait(1);
}catch(Exception e){}
paintNextNumber();
private void paintNextNumber(){
if(x<30000){
x++;
b=String.valueOf(x);
mc.doPaint = true; //signals that next number can be painted
public void pauseApp() {
public void destroyApp(boolean unconditional) {
class MyCanvas extends Canvas implements Runnable{
Image buf = null;
Graphics bg = null;
public boolean doPaint = true;
public MyCanvas(){
buf = Image.createImage(getWidth(),getHeight());
bg = buf.getGraphics();
public void paint(Graphics g){
bg.setColor(255,255,255);
bg.fillRect(0,0,getWidth(),getHeight());
bg.setColor(0);
bg.drawString(b,10,10,0);
g.drawImage(buf,10,10,Graphics.TOP|Graphics.LEFT);
// Callback for next number to be painted
MyMIDlet.this.callbackPaintDone();
public void run(){
while(true){
if(doPaint){ //only paints when a number has been painted, and next one is ready to be painted
doPaint = false;
repaint();
serviceRepaints();