A sterling idea John.  For more on that concept..
<http://www.physci.org/codes/sscce.jsp>

Well, apart from the naming, the real code is the same, with the factory
method being static.

class VisualizationFactory {

    enum DiagramType {
    LINE_DIAGRAM,
    BAR_DIAGRAM,
    COL_DIAGRAM
    }

    public static Diagram createDiagram( DiagramType type ) {
    switch( type ) {
    case LINE_DIAGRAM:
       System.out.println( "Line Diagram requested" );
       return new LineDiagram();
    default: // the other classes don't yet exist
       System.out.println( "unexpected" );
       break;
    }

    return null;
    }

}

public abstract class Diagram {

    public abstract void paint( Graphics g );
    public abstract void foo(); // for testing, it is never actually
called, though invoked!

}

    import java.awt.*;

public class LineDiagram extends Diagram {

    public void paint( Graphics g ) {
    System.out.println( "painting line diagram" );
    }

    public void foo() {
    System.out.println( "foo" );
    }

}

public class MainWindow extends JFrame {

    public static void main( String[] args ) {
    //  [...]
    Diagram diagram =
VisualizationFactory.createDiagram(VisualizationFactory.DiagramType.LINE_DIAGRAM);

    VisualizationFrame intFrame = new DiagramFrame("Viz", diagram );

    }

}

The newly created diagram is passed to a DiagramFrame, which is a
JInternalFrame and supposed to draw diagrams.
Now inside this DiagramFrame's paint() method:

class DiagramFrame extends VisualizationFrame {

    public DiagramFrame( String title, Diagram diagram ) {
    super( title );
    assert( diagram != null );
    this.diagram = diagram;
    }

    public void paint( Graphics g ) {
    super.paint( g );

    //Graphics2D g2d = (Graphics2D) g;
    //diagram.paint( g );
    System.out.println( "frame paint" );
    diagram.foo();
    }

    private Diagram diagram;

}

The program outputs "frame paint" on each window update, but the text I
am outputting in foo() is NEVER displayed. It is however displayed as
soon as I for example replace the call to the factory's creation method
with a normal "new LineDiagram()". Then everything works as expected.
It also works when I make the creation method non-static and then
instantiate the factory class first.

Odd, isn't it.