JAVA ME - Problems compiling and running (using Eclipse)

Question

Hello,
I am new to Java ME and I am trying to run a copied HelloMIDlet application. I am getting following error when I am trying to run the application:
Running with storage root C:\Users\Niklas\j2mewtk\2.5.2\appdb\MediaControlSkin
Running with locale: Swedish_Sweden.1252
Running in the identified_third_party security domain
java.lang.NullPointerException
     at javax.microedition.lcdui.Item.addCommandImpl(+11)
     at javax.microedition.lcdui.StringItem.addCommandImpl(+11)
     at javax.microedition.lcdui.Item.addCommand(+11)
     at HelloMIDlet.<init>(+99)
     at java.lang.Class.runCustomCode(+0)
     at com.sun.midp.midlet.MIDletState.createMIDlet(+34)
     at com.sun.midp.midlet.Scheduler.schedule(+52)
     at com.sun.midp.main.Main.runLocalClass(+28)
     at com.sun.midp.main.Main.main(+80)
Execution completed.
3415817 bytecodes executed
17 thread switches
1667 classes in the system (including system classes)
17760 dynamic objects allocated (533540 bytes)
2 garbage collections (459436 bytes collected)And the applicaiton:
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class HelloMIDlet extends MIDlet
       implements CommandListener {
  // The exit command
  private Command exitCommand;
  // The display for this MIDlet
  private Display display;   
  // create a ticker
  private Ticker hi = new Ticker("J2ME is cool");
  public HelloMIDlet() {
    display = Display.getDisplay(this);
    exitCommand = new Command("Exit", Command.SCREEN, 2);
  public void startApp() {
    TextBox t = new TextBox("Hello MIDlet",
                "Wireless Internet", 256, 0);
    t.addCommand(exitCommand);
    t.setCommandListener(this);
    t.setTicker(hi); // set the ticker
    display.setCurrent(t);
  public void pauseApp() { }
  public void destroyApp(boolean unconditional) { }
  public void commandAction(Command c, Displayable s) {
    if (c == exitCommand) {
      destroyApp(false);
      notifyDestroyed();
}I did try to remove as much code as possible still being able to compile it. Exactly the same type of error was presented still...
I have another MIDlet in the same projects that works fine.
What is the problem?
Thank you in advance!
Best Regards,
Niklas

Answer 1

java.lang.NullPointerException
     at HelloMIDlet.<init>(+99)
...Try to modify your code about as follows:
  private Ticker hi;  // initialize ticker in startApp
/* don't override the MIDlet constructor
  public HelloMIDlet() {
  public void startApp() {
    // initialize all MIDP UI stuff in startApp
    hi = new Ticker("J2ME is cool");
    display = Display.getDisplay(this);
    exitCommand = new Command("Exit", Command.SCREEN, 2);
    TextBox t = new TextBox("Hello MIDlet",
                "Wireless Internet", 256, 0);
    t.addCommand(exitCommand);
    t.setCommandListener(this);
    t.setTicker(hi); // set the ticker
    display.setCurrent(t);
//...The problem might be caused by initializing MIDP UI stuff prior to entering startApp method. I also think that overriding MIDlet constructor is not quite a good idea. Check [MIDP tutorials (Google search shows plenty)|http://www.google.com/search?q=MIDP+tutorials] if you're interested to know more details on that.