Thanks for the answers!
Sorry, I indeed read it correctly, but missed typing one word...
Ok, I think I understand now. Moving on a plain Widget could work ok, because there is no "layouting code" in the Widget, as it would be in BoxLayout or similar, right?
I think DesktopArea/ResizableFrame does not fit my needs, because I don't want to let the user change size and position of the widgets, I only do want adjust this from code...
Another (quite theoretical) question: what kind of impact does the size of a (plain) Widget have on it's children? I've encountered no difference at all, neither visibility, nor alignment or something?
As far as my understanding goes, the size of some Widget only has meaning to itself (rendering etc.)... and of course e. g. a BorderLayout's size determines the size and position of its children... (because layout() is overriden).
I ask this because you mentioned the size of the root widget, which automatically has size of the viewport as you explained. But if it would be smaller (hypothetically)... Or, to be more realistic, let's say we add another (plain) Widget to the root widget and then a Button as child of this second Widget. If the widget would be very small, the Button is visible anyways, right?