Java.lang.InstantiationException / XMLEncoder error what's that?

Question

Hello there!
After I received so much help from Joachim yesterday, I think I have to bother you again with a problem:
I wrote this application for testing purposes. This app only counts an interger up and down from 0 to 10 and displays the value in a JTextBox as Strings like int = 3 means: "three". These Strings are all in an array. Additionally, I have implemented a localisation (german and english language). I read these properties from a .properties File and change the label of the buttons and the language of the value-strings. Also I serialize my app using the Beans-persistence.
So far so good but I get an error in the following situation:
When I change the language using a JMenuBar-entry and then close the app-window (now the app status is written to a xml-file (persistence)) I get:
java.lang.InstantiationException: javax.swing.PopupFactory$HeavyWeightPopup$1
Continuing ...
java.lang.Exception: XMLEncoder: discarding statement XMLTest.addWindowListener(PopupFactory$HeavyWeightPopup$1);
Continuing ...The status is saved to the file and the reconstruction from the file works fine. But this error annoys me and I have to get rid of it. More information: when I run the app and foolin' around with the buttons BUT DON'T CHANGE the language, the error doesn't appear.
The app is working fine, but what does this error mean? I'm pretty new to Java and google doesn't help me...
Here is my code: http://pastebin.com/m6b58751c
Thanks for having a look...
Thomas
Edited by: king-al on Feb 10, 2009 11:57 AM

Answer 1

ejp wrote:
The error occurred because the XMLEncoder couldn't instantiate another XMLTest object. That would be because it didn't have a no-args constructor, which it must have to qualify as a Java Bean, which it must do to be XMLEncodable (or else have a PersistenceDelegate that can instantiate it). When you changed it to have-a JFrame instead of be-a JFrame you probably changed the constructor too.Okay BUT: I have a PersistenceDelegate because I have a args-constructor:
public class XMLTestPersistenceDelegate extends DefaultPersistenceDelegate{
        @Override
    protected Expression instantiate(Object oldInstance,Encoder out){ // fure den übergabewert am kontruktor
        XMLTest t=(XMLTest)oldInstance;
        return new Expression(oldInstance,XMLTest.class,"new",new Object[]{t.width});
        @Override
    protected void initialize(Class<?> type, Object oldInstance, Object newInstance, Encoder out){
        super.initialize(type, oldInstance, newInstance, out);
        XMLTest t=(XMLTest)oldInstance;
        out.writeStatement(new Statement(
                oldInstance,"endisFunction", new Object[]{}));
        for(int i=0;i<t.value;i++) // so oft plusFunction aufrufen, wie value groß ist
            out.writeStatement(new Statement(
                oldInstance,"plusFunction",new Object[]{}));
        if(!t.enabled)
           out.writeStatement(new Statement(
                oldInstance,"endisFunction", new Object[]{}));
}The width value is the int-value of the width of my JTextField. The Statements are for some other properties of my object.
Right now, I still don't understand why it doesn't work when my Class XMLTest ist extended from JFrame.
And when I changed it to have-a JFrame I only changed some properties in my constructor of the JFrame i.e.: this.setVisible(true) to f.setVisible(true)... but nothing more.
Edited by: king-al on Feb 11, 2009 3:44 AM