First download this one:
WithoutGUIDesigner.zip

There you can see, how to use Jabaco-controls with events without GUI-Designer.

Thanks to A1880. He have mentioned at
UserControl and Graphics2d
that it is possible to use nested classes in Jabaco as normal classes. So it is possible to use and create nested classes in Jabaco.

WithoutGUIDesigner.zip have some subdirectories.

In 01-JabacoOriginal
you can see a GUI-designer created Jabaco program#

In 01-PortedToJava
it is the same program, only with Java as Syntax. It calls the same Jabaco-Controls and Events.

In 03-BackportToJabacoWithoutGUIDesigner
you can see it backported to Jabaco. All (Controls and Events) are only written as text

In 04-MixOfOriginalAndBackport there are only the Sliders hand-written. It shows how you can use controls, which currently are not supported by the GUI-designer can be used the other way around.

Im "Simple" is a very simple example, which is easy to understand and easy to read.