Company-mode
http://company-mode.github.io
in buffer completion framework for emacs
Eclim
http://eclim.org/index.html
Eclim provides the ability to access Eclipse features (code
completion, searching, code validation, and many more) via the
command line or a local network connection, allowing those
features to be integrated with your favorite editor. Eclim
provides an integration with Vim, but third party clients have
been created to add eclim support to other editors as well (emacs,
sublime text 2, textmate).
Emacs eclim
https://github.com/senny/emacs-eclim
Eclim is an Eclipse plugin which exposes Eclipse features through
a server interface. When this server is started, the command line
utility eclim can be used to issue requests to that server.
http://www.skybert.net/emacs/java/
可以看看以上套件合在一起用的样子
把Emacs变成一个完整的java IDE...