Solution for NullPointerException in "AWT-EventQueue-0"?

Question

Hi,
At the moment I'm working on a program that will display the state of processes of machines. I have chosen to work with the MVC pattern, as the program relies heavily on the screen. While (test) running the program I see the (sometimes more then) occasional NullPointerException occurring. In *one* of many threads on this issue it was suggested to:
Darryl.Burke wrote:
Use SwingUtilities.invokeLater (...) or SwingUtilities.invokeAndWait (...) to get rid of the Exception.I already used invokeLater( as shown in this piece of code:
     private static void createAndShowGUI() {
          model = new MyModel();
          view = new MyView (model, "My System");
     public static void main (String [] args) {
          javax.swing.SwingUtilities.invokeLater(new Runnable() {
               public void run() {
                    createAndShowGUI();
     }Thinking the previous piece of code starts both the Model implementation part of MVC AND the View implementation part in the same thread, I changed the code to:
     private static void createAndShowGUI() {
          view = new MyView (model, "My System");
     public static void main (String [] args) {
          model = new MyModel();
          javax.swing.SwingUtilities.invokeLater(new Runnable() {
               public void run() {
                    createAndShowGUI();
     }If I interpreted invokeLater() correctly, both model and view are now started in different threads. It still starts. It still runs. I still have all the functionality. But I also still get the same NPE. :-[
Any suggestions?
Abel.

Answer 1

Here's an example. In my code, I want to dynamically update the text of a subclass of JLabel. That MUST be done inside Swing's Event thread. I have an inner class I call "PrintHelper" that I call when I want to update my JLabel text. So rather than calling setText(text) on my JLabel, I can call printHelper.out(text) from inside the subclass, or I call ioUpdate(text) from another class.
// Inside my JLabel subclass...
class printHelper implements Runnable {
     private String text;
     public void out(String text) {
          this.text=text;
          if (EventQueue.isDispatchThread()) run();
          else
               try {
                    EventQueue.invokeAndWait(this); // else schedule it
               } catch (InterruptedException e) {
                    e.printStackTrace();
               } catch (InvocationTargetException e) {
                    e.printStackTrace();
      * Sets the text of the label.  If the text is empty, it prints a space so the label
      * occupies space.
     public void run() {
          modifyLabelBasedOnText(); // Changes color based on text content; code not included
          if (this.text == null ) { setText (" -null-        Null text!"); return; };
          if (this.text.equals("")) setText(" ");
          else setText(this.text);
private printHelper printHelper=new printHelper();
* Update the text of this label.  If the text is empty, it will print a space so that at least
* the label occupies space.
* @param stdout
public void ioUpdate(String stdout) {
     printHelper.out(stdout);
}