Implementation class memeber variables are null

Question

I have faced this before and I never could figure it out and now I really need to know why this happens. Please see the following pseudo code:
// Parent
public class MyAbstractPanel extends JPanel{
   public MyAbstractPanel{
     try{
       jbInit();
     }catch(Exception e){
       // Take measure
  public abstract jbInit() throws Exception;
// Implementor
public class MyImplementor extends MyAbstractPanel{
  public JTextArea textArea = new JTextArea();
  public jbInit() throws Exception {
     // do stuff
     textArea .setText("Test Message");  <<------- THROWS NULL POINTER EXCEPTION HERE
// Factory
public class FrameFactory{
  private static myImplementor;
  public static MyAbstractFrame getMyplementor(){
    if (myImplementor == null){
      myImplementor = new MyImplementor();
    return myImplementor;
  // Client implementation
  public static void main(String[] args) throws Exception {
    JFrame frame = ....
    frame.add(FrameFactory.getMyplementor());
}If I initialize the textArea inside the jbInit() method in MyImplementor class then it fixes the issue but if I put initialize on accessor level, it never get initialized. Is it JDK bug or there something I have missed on inheritance rule.
I am currently trying to fix and existing application it's will be a real big job for me to move all the initialize expression from the header to jbInit() or in any initialize method.Any idea why?

Answer 1

This is the wrong forum, but I'll answer your question anyway.
There is a default constructor for MyImplementor that is compiler generated. It looks like this:
public MyImplementor() {
  super();
  textArea = new JTextArea();
}MyAbstractPanel() calls jbInit(), which you've overriden in MyImplementor.
See the problem?
As a trivia note, C++ handles this by not dispatching method calls virtually during object construction. Less flexible, but safer.
God bless,
-Toby Reyelts