While I try to do most of my editing from Emacs, occasionally I will
find myself using the Eclipse Java editor. One of the more convenient
niceties, in the absence of auto-fill-mode, is having the print-margin
displayed. This is a useful feature in its own right, i.e. show a 1
pixel background line in Emacs where the right margin is set. Needless
to say, I have not a clue how to implement it.