Wow, that is cool, much better than what I did.
Thank you Michael very much for the help. I really appreciate it.
Actually I was thinking to use GridBagLayout, which only needs one layer to create this UI, but it looks complicated for me.
The reason I want to use it is that I am not sure if I want to update panel 3 which will show a scanned image, do I also need to update holdingPanel 2 which hold panel 3? Thanks.