🚀 go-pugleaf

The reason that you can edit the abstract class in the GUI designer is that
JBuilder instantiates the base class and uses it in the designer (given that
the class you're designing may not compile, JBuilder can't instantiate it
but can manage the components).  However, when you create a class derived
from your abstract class, JBuilder tries to instantiate the base class but
can't because it is declared as abstract.

The alternative is to create a proxy class that can be instantiated in place
of your abstract base class.  For details, open index.html in the JBuilder
installation directory, go to the JBuilderX release notes, and search for
the word "proxy".

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"Jan Sundin" <jan@sundin.com> wrote in message
news:40727548$1@newsgroups.borland.com...
>
> Hi
> I'm trying to migrate code from an existing user interface to JBuilder X.
I have encountered a problem that I have tracked down to the following:
> My class hierarchy typically has an abstract super class that extends
JInternalFrame. This class adds some behaviour (both visual and nonvisual).
Editing this abstract class in the gui builder works fine (impressive,
wouldn't have expected that to work).
>
> Now, the problem is that concrete _subclasses_ to the abstract class are
not editable in the gui-builder! When trying to show them in the editor the
following message is displayed in the Designer-message panel:
>
> Failed to create live instance for variable 'this'. null
> class java.lang.NullPointerException null
>
> To "stdout" the following stacktrace is printed:
> java.lang.NullPointerException
>         at com.borland.jbuilder.designer.ui.ModelNode.<init>(Unknown
Source)
>         at com.borland.jbuilder.designer.ui.Model.<init>(Unknown Source)
>         at com.borland.jbuilder.designer.ui.UIDesigner.annotate(Unknown
Source)
>         at com.borland.jbuilder.designer.DesignerManager.a(Unknown Source)
>         at com.borland.jbuilder.designer.DesignerViewer.openImpl(Unknown
Source)
>         at com.borland.jbuilder.designer.DesignerViewer.open(Unknown
Source)
>         at com.borland.jbuilder.designer.DesignerViewer.changeUrl(Unknown
Source)
>         at
com.borland.jbuilder.designer.DesignerViewer.viewerActivated(Unknown Source)
>         at com.borland.jbuilder.designer.h.run(Unknown Source)
>         at
java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:178)
> ...
>
> Making the super-class concrete makes the problem disaapear but that will
force me to redesign my existing classhierarcy. Is this a bug?
>
> I'm using JBuilder (Developer Trial) 10.0.176.0
>
> TIA,
>
> Jan Sundin
>