最近看了《J2ME开发大全》书有个使用command对象的在线帮助程序的例子。用wtk104编译可以通过，但是不能运行。请大家看看怎么回事？发表意见。
程序清单：
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class OnlineHelp extends MIDlet implements CommandListener
{
private Display display;
private Command back;
private Command exit;
private Command help;
private Form form;
private TextBox helpMesg;
public OnlineHelp()
{
display = Display.getDisplay(this);
back = new Command("Back",Command.BACK, 2);
exit = new Command("Exit",Command.EXIT, 1);
help = new Command("Help",Command.HELP, 3);
form = new Form("Online help Example");
helpMesg = new TextBox("Online Help","press Back to return to the previous screen or press Exit Exist to close this program.", 81, 0);
helpMesg.addCommand(back);
form.addCommand(exit);
form.addCommand(help);
form.setCommandListener(this);
helpMesg.setCommandListener(this);
}
public void startApp()
{
display.setCurrent(form);
}
public void pauseApp()
{
}
public void destroyApp(boolean unconditional)
{
}
public void commandAction(Command command,Displayable displayable)
{
if (command == back)
{
display.setCurrent(form);
}
else if (command == exit)
{
destroyApp(false);
notifyDestroyed();
}
else if (command == help)
{
display.setCurrent(helpMesg);
}
}
}

运行出错信息；
Unable to create MIDlet OnlineHelp

java.lang.IllegalArgumentException

at javax.microedition.lcdui.TextBasic.<init>(+104)

at javax.microedition.lcdui.TextBox.initializeTextBasic(+11)

at javax.microedition.lcdui.TextBox.<init>(+45)

at OnlineHelp.<init>(+86)

at java.lang.Class.runCustomCode(+0)

at com.sun.midp.midlet.Selector.commandAction(+50)

at javax.microedition.lcdui.List.keyPressed(+71)

at javax.microedition.lcdui.Display$DisplayAccessor.keyEvent(+147)

at com.sun.kvem.midp.lcdui.EmulEventHandler$EventLoop.run(+295)