Boundary for comment box

Answer 1

This can be a little bit tricky. When you need semitransparent border it will be pain. If not, it is easy. Just use popup with appropriate components and mouse listener to listen on mouse events occurred over active borders.

Answer 2

I would perhaps look at using JXLayer for this. It looks like what you're trying to do here is paint some context outside the of component's bounds. This is the kind of thing JXLayer excels at.