Is it possible at all to have one component superimposed (or stacked) over another in Swing?
I’m thinking about having a progressbar (in the foreground) which would be sitting right on top of a JTable (in the background) while the table initialisation is ongoing…
Yes, there are a few ways of doing this.
This could be done by adding it to the glass pane but this will normally block your UI.
I would look into JXLayer which allows you to wrap components to perform additional paint jobs. There is also a JBusyComponent which relies on this library that probably does what you want.