URGENT THREAD HELP NEED!!

Question

Hi,
I am trying to attach a very basic phone file browser (based on the one bundled with the J2ME toolkit) to an interface and am have great trouble.
I think it is to with not using any threads, which i have no idea about. I searched and read some articles to help, but it has not aided the problem and any changes that i make..make no difference.
I have two classes; one that deals with just transversing through the file system FileSystemBrowser and the other is the GUI that displays the file system graphically called TextReader (ignore the name it will change when the program is finished).
The Toolkit keeps throwing this message at me every time i run the classes in the emulator:
Warning: To avoid potential deadlock, operations that may block, such as
networking, should be performed in a different thread than the
commandAction() handler.
here is my interface class code:
import java.lang.Thread;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.StringItem;
import javax.microedition.lcdui.List;
import javax.microedition.lcdui.Choice;
import javax.microedition.lcdui.Image;
import javax.microedition.lcdui.Alert;
import javax.microedition.lcdui.AlertType;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Display;
import javax.microedition.midlet.MIDlet;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import java.util.*;
import java.io.*;
import javax.microedition.io.file.IllegalModeException;
public class TextReader extends MIDlet implements CommandListener
private FileSystemBrowser MyBrowser;
// Options in loadOptions list.
private String[] loadChoice = {"Locate File", "Favourites Folder"};
// individual icon images.
private Image dirIcon, fileIcon, backIcon;
// icons to be displayed on screen.
private Image[] icons;
/* separator character as defined by FC specification */
private final static char SEP = '/';
private Command select = new Command("SELECT", Command.OK, 1);
private Command exit = new Command("EXIT", Command.EXIT, 1);
public TextReader()
MyBrowser = new FileSystemBrowser();
try
dirIcon = Image.createImage("/icons/dir.png");
catch (IOException e)
dirIcon = null;
try
fileIcon = Image.createImage("/icons/file.png");
catch (IOException e)
fileIcon = null;
icons = new Image[] {fileIcon, dirIcon};
private void loadMenu()
List loadOptions = new List("Load Options:", List.IMPLICIT, loadChoice, null);
loadOptions.addCommand(select);
loadOptions.addCommand(exit);
loadOptions.setCommandListener(this);
Display.getDisplay(this).setCurrent(loadOptions);
private void showCurrDir()
Enumeration e;
List browser = new List("Locate File:", List.IMPLICIT);
browser.append(MyBrowser.getCurrentDir(), null);
System.out.println("got here");
browser.append("Back", backIcon);
try
e = MyBrowser.listContent();
while (e.hasMoreElements())
String fileName = (String)e.nextElement();
//if (fileName.charAt(fileName.length()-1) == SEP)
if(MyBrowser.isDirectory(fileName))
// This is directory
browser.append(fileName, dirIcon);
else
// This is a regular file
browser.append(fileName, fileIcon);
browser.addCommand(select);
browser.addCommand(exit);
browser.setCommandListener(this);
Display.getDisplay(this).setCurrent(browser);
catch(IOException ex)
Alert alert = new Alert("Error",
"You are not authorized to access the restricted API",
null, AlertType.ERROR);
alert.setTimeout(Alert.FOREVER);
Form form = new Form("Cannot access FileConnection");
form.append(new StringItem(null,
"You cannot run this MIDlet with the current permissions. "
+ "Sign the MIDlet suite, or run it in a different security domain"));
form.addCommand(exit);
form.setCommandListener(this);
Display.getDisplay(this).setCurrent(alert, form);
//throw new IllegalModeException("Directory is Read Restricted or Target is a File");
private void loadFile(String fileName)
if(MyBrowser.isDirectory(fileName) || fileName.equals("Back"))
try
MyBrowser.transverseDir(fileName);
showCurrDir();
catch(Exception e)
System.out.print("Alert: thrown exception");// fill this in.
else
// Code here will open a file when implemented.
public void commandAction(Command com, Displayable dis)
if(com == select)
if("Load Options:".equals(dis.getTitle()))
showCurrDir();
if("Locate File:".equals(dis.getTitle()))
List curr = (List)dis;
String fileName = curr.getString(curr.getSelectedIndex());
loadFile(fileName);
if(com == exit)
if("Load Options:".equals(dis.getTitle()))
notifyDestroyed();
if("Locate File:".equals(dis.getTitle()))
loadMenu();
public void startApp()
loadMenu();
public void pauseApp()
public void destroyApp(boolean unconditional)
My other class FileSystemBrowser has two main methods that are used :
public void transverseDir(fileName)
public Enumeration listContent()
The first method transverseDir(fileName) just adds and removes bits of a file path represented by a string. Nothing to processor intensive. The other method listContent() uses FileConnection methods such as (FileConnection)Connector.open("blah blah") to connect to an actual directory and FileSystemRegistry.listRoots(); to list the inital root files of a phones filesystem.
I've tried implementing threads on them but it has made no difference and i dont know if im doing it right or whether they even need to be threaded, because the problem may be in the interface. But if this is so i still dont know where it is and how to fix it.
CAN ANYONE HELP PLEASE?
I Am doing this as part of my final year project as a university student.
Thanks in advance.

Answer 1

Thanks for the replies guys,
Thats really good stuff to know, but im still not sure what to place inside the thread? (e.g. methods if this is the case which ones or which class), do i need to synchronise anything? if so..what needs to be synchronised? I have read some articles on threading and understand the concepts but i am at a loss when it comes to actual implementing the thread correctly. Because when i have tryed to use threads the same error is thrown:
Warning: To avoid potential deadlock, operations that may block, such as
networking, should be performed in a different thread than the
commandAction() handler.
Can can one give me further directions on where they think i need to use the threads and synchronisation and how?
Thanks in advance.
birdeboy