Java Runtime Exception

when i run my application i get the following error:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at javax.swing.text.FlowView$FlowStrategy.layoutRow(FlowView.java:546)
    at javax.swing.text.FlowView$FlowStrategy.layout(FlowView.java:460)
    at javax.swing.text.FlowView.layout(FlowView.java:184)
    at javax.swing.text.BoxView.setSize(BoxView.java:380)
    at javax.swing.text.BoxView.updateChildSizes(BoxView.java:349)
    at javax.swing.text.BoxView.setSpanOnAxis(BoxView.java:331)
    at javax.swing.text.BoxView.layout(BoxView.java:691)
    at javax.swing.text.BoxView.setSize(BoxView.java:380)
    at javax.swing.plaf.basic.BasicTextUI$RootView.setSize(BasicTextUI.java:1702)
    at javax.swing.plaf.basic.BasicTextUI.modelToView(BasicTextUI.java:1034)
    at javax.swing.text.DefaultCaret.repaintNewCaret(DefaultCaret.java:1291)
    at javax.swing.text.DefaultCaret$1.run(DefaultCaret.开发者_如何学编程java:1270)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

as the error does not mention any of my classes, how would i go about in finding what is causing this?

if i try: public void notifyChatMessage(String message){...} the error goes away (NOT).

edit: upon further testing it turns out the above generates the error also.

but if i try: public void notifyChatMessage(Object message){...} the error is reported.

please advise.

EDIT:

        public void notifyChatMessage(String message){


         AppMessage appMessage = new AppMessage(AppMessage.Target.Chat, message);
         setChanged();
         notifyObservers(appMessage);

     }

AppMessage:

public class AppMessage implements Serializable {

/**
 * Message header for target: game, chat
 */
public enum Target {
    Game, Chat
}

/**
 * Holds target
 */
public Target target;

/**
 * Holds state message
 */
public Object message;

/**
 * Construct using parameter data
 * @param target
 * @param message
 */
public AppMessage(Target target, Object message){

    this.target = target;
    this.message = message;

}

}

EDIT: even with the error report the program continues to run and i cannot see any lack of performance ie. error in running which is making the task of localizing the problem more complex.

EDIT: when i run it through the debugger in netbeans i get: Debugger stopped on uncompilable source code.

EDIT: the exception is being thrown because of cross thread GUI updates. investigating invokeLater and invokeAndWait for solution.

SOLUTION: invokeAndWait

The call javax.swing.text.FlowView$FlowStrategy.layoutRow(FlowView.java:546) is trying to process something that is NULL. Looking at its signature. layoutRow(FlowView fv, int rowIndex, int pos) the only thing that can be NULL is FlowView fv since the int primatives can't be NULL. So without having the code to run and step debug thru, I would say that somewhere something is either not setting FlowView or setting it to NULL.

Use the source... start with javax.swing.text.FlowView line 546