NullPointerException - Can't figure this out

[Frank Manno]

Hi All,
I'm learning J2ME, and am absolutely loving it!!
I ran into a problem with a sample application I'm working on... I cannot seem to get the MIDlet to run. I keep receiving a NullPointerException. This is the code I'm using:

  
/*
 * NonInteractiveGauge.java
 *
 * Created on July 3, 2003, 8:04 PM
 */
package InteractiveGauge;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.util.Timer;
import java.util.TimerTask;
/**
 *
 * @author  Frank
 * @version
 */
public class NonInteractiveGauge extends javax.microedition.midlet.MIDlet implements CommandListener{
    
    private Display display;            // Display obj
    private Form fmMain;                // Main form
    private Command cmExit;             // Exit command
    private Command cmStop;             // Stop command
    private Gauge gaProgress;           // Progress gauge/meter
    private Timer tm;                   // Timer 
    private TimerTask tt;               // Timer task to run
    
    public void NonInteractiveGauge(){
        
        System.out.println("Inside Constructor");
        
        display = Display.getDisplay(this);
        
        // Create commands and gauge
        cmExit = new Command("Exit", Command.EXIT, 1);
        cmStop = new Command("Stop", Command.STOP, 1);
        
        gaProgress = new Gauge("Download Progress", false, 20, 1);
        
        // Create form, add commands and listener
        fmMain = new Form("");
        fmMain.append(gaProgress);
        fmMain.addCommand(cmStop);
        fmMain.addCommand(cmExit);
        fmMain.setCommandListener(this);
    }               
    
    public void startApp() {
        try{
            display.setCurrent(fmMain);
            System.out.println("Form Set");
            // Create a timer that fires off every 1000 milliseconds
            tm = new Timer();
            System.out.println("Timer Created");
            tt = new DownloadTimer();
            System.out.println("Download Timer Created");
            tm.scheduleAtFixedRate(tt, 0, 1000);
            System.out.println("Timer Scheduled");
        }
        catch (Exception ex){
            System.out.println("Error: " + ex.toString());
        }
    }
    
    public void pauseApp() {
    }
    
    public void destroyApp(boolean unconditional) {
    }
    
    public void commandAction(Command c, Displayable s){
        
        if (c == cmExit){
            
            destroyApp(false);
            notifyDestroyed();
        }
        else if (c == cmStop){
            tm.cancel();
            fmMain.removeCommand(cmStop);
            fmMain.addCommand(cmExit);
            gaProgress.setLabel("Download cancelled!");
        }
    }
    
    /***************
     * New Class - handle timer task
     ***************/
    private class DownloadTimer extends TimerTask{
        
        public final void run(){
            
            // Is current value of gauge less than max?
            if (gaProgress.getValue() < gaProgress.getMaxValue()){
                gaProgress.setValue(gaProgress.getValue() + 1);
            } 
            else {
                // Remove the stop command and replace w/ exit - download complete
                fmMain.removeCommand(cmStop);
                fmMain.addCommand(cmExit);
                gaProgress.setLabel("Download Complete!");
                
                // Stop timer
                cancel();
            }
        }
    }
}

And the error I receive is this:
startApp threw an Exception
java.lang.NullPointerException
java.lang.NullPointerException
at InteractiveGauge.NonInteractiveGauge.startApp(+8)
at javax.microedition.midlet.MIDletProxy.startApp(+7)
at com.sun.midp.midlet.Scheduler.schedule(+225)
at com.sun.midp.dev.DevMIDletSuiteImpl.schedule(+7)
at com.sun.midp.Main.runLocalClass(+20)
at com.sun.midp.Main.main(+68)

Any help would be greatly appreciated... The book's code is IDENTICAL, so I can't figure out what it is that I'm missing...
I'm running it using WTK2.0...

Thanks!
Frank

[Hemant Sareen]

Hi Frank:
Please remoive "void" from the statement
public void NonInteractiveGauge()
so that it becomes the constructor for this Midlet class...it is taking it as a method now...

[Frank Manno]

Hemant,
Thank you very much... I knew it had to have been something I overlooked... I can't believe I hadn't noticed that one!
Thanks again!

[Frank Manno]

Alright,
I'm having another problem now... I figured that I'd just continue this thread, rather than starting a new one... My problem is now related to reading image files located on my drive. This is the code I'm running:

public class ImplicitList extends javax.microedition.midlet.MIDlet implements CommandListener {
    
    private Display display;        // Display obj
    private List lsDocument;        // Main document list
    private Command cmExit;         // Exit command
    private Command cmAdd;          // Add command
    
    public ImplicitList(){
        
        display = Display.getDisplay(this);
        
        // Create commands
        cmExit = new Command("Exit", Command.EXIT, 1);
        cmAdd = new Command("Add", Command.SCREEN, 1);
        
        try{
            
            // Create array of image objects
            Image images[] = {Image.createImage("/res/ff.png"), Image.createImage("/res/rr.png"),
                              Image.createImage("/res/new.png")};
                              
            // Create array of corresponding string objects
            String options[] = {" Next", " Previous", " New"};
            
            // Create a list using arrays, add commands and listeners
            lsDocument = new List("Document Options", List.IMPLICIT, options, images);
            lsDocument.addCommand(cmAdd);
            lsDocument.addCommand(cmExit);
            lsDocument.setCommandListener(this);
        }
        catch (java.io.IOException e){
            System.out.println("1) Unable to locate or read .png files: " + e.toString());
        }
    }            
    
    public void startApp() {
        display.setCurrent(lsDocument);
    }
    
    public void pauseApp() {
    }
    
    public void destroyApp(boolean unconditional) {
    }
    
    public void commandAction(Command c, Displayable s){
        
        // If an implicit list generated the event
        if (c == List.SELECT_COMMAND){
            
            switch (lsDocument.getSelectedIndex()){
                
                case 0:
                    System.out.println("Next");
                    break;
                    
                case 1:
                    System.out.println("Previous");
                    break;
                    
                case 2:
                    System.out.println("New");
                    break;
                    
                default:
                    System.out.println("New Element");
            }
        }
        else if (c == cmAdd){
            try{
                // Add a new element.  Using size() as the insertion point,
                // the elemtn will be appended to the end of the list
                lsDocument.insert(lsDocument.size(), " Delete", Image.createImage("res/delete.png"));
            }
            catch (java.io.IOException e){
                System.out.println("Unable to locate or read .png file: " + e.toString());
            }
        }
        else if (c == cmExit){
            
            destroyApp(false);
            notifyDestroyed();
        }
    }                    
}

The problem is that the IOException is ALWAYS being thrown... And it seems as though it's being thrown here:

            Image images[] = {Image.createImage("/res/ff.png"), Image.createImage("/res/rr.png"),
                              Image.createImage("/res/new.png")};

the images I have area located in the res/ directory located in the same directory as my MIDlet. I've also tried taking out the first slash so that the path is: "res/ff.png", etc., and it doesn't seem to matter.
Any ideas on this one would be appreciated!
Thanks!

[Michael Yuan]

The "res/" directory needs to be just under the top level directory of your JAR package.

JAR file
  res/
  com/
    mycompany/
      mymidlet.class

[Frank Manno]

Originally posted by Michael Yuan:
The "res/" directory needs to be just under the top level directory of your JAR package.

JAR file
  res/
  com/
    mycompany/
      mymidlet.class

Hi Michael,
So the resource directory is actually two levels below where the MIDlet is located? Does this also apply when the MIDlet is NOT packaged in a JAR file? I get this error when trying to run it from the SunOne Studio...

Thanks,
Frank

[Hemant Sareen]

Hi Frank:
You don't have to specify 'res' in the path just use "/image_name"..
Hope it works..

[Greg Schwartz]

I had the same problem with images when I had a path such as /res/image.png Your SDK should default to the /res directory when looking for image files so you only need to put /image.png as the path, as Hermant stated.

[Frank Manno]

Thanks for the tip... I'll keep that in mind! Can the "res" directory not be in the same folder as the MIDlet, or is it just better practice to keep them seperated in their own folders?
Thanks!

[Greg Schwartz]

The sdk's that I've been using have a directory for each J2ME application. The jar/jad files reside in this main directory. Also in this directory are "class", "rsc" (the equivalent of your "res") and "src" folders. All of my image files are in the "rsc" folder that is within the MIDlets main folder. Hope this helps.

Greg