By default, Emacs just provide some simple auto complete. For example, Alt + /, it will invoke ‘dabbrev-expand’.
and ‘dabbrev-expand’ is to find and complete what you enter once it find match words in all ‘buffer’ opened.

xrefactory is excellent commerce plugin for emacs, xrefactory is free for C/Java.

Here is how to enable xrefactory in emacs.

http://www.xref.sk/xrefactory/downloads/1.6.10/xrefactory-1.6.10-src.tgz

uncompress the tgz file，tar zxvf xrefactory-1.6.10-src.tgz

go into folder ‘xref-any’ , type command ‘make’, it will compile and finish to get ‘xref’

In .emacs file, add following code (replace ‘path/to’ to the path you want)

(add-to-list ‘load-path “/path/to/xref-any/env/emacs”)
(add-to-list ‘exec-path “/path/to/xref-any/src”)
(load “xrefactory”)
;;(load “/path/to/env/emacs/xrefactory.el”)

run ‘M-x eval-current-buffer’ , Now you could use xrefactory , Press ‘F8’ key to call ‘xref-completion’

xref is very powerfull, but we still has some other tools such as ‘gccsense, gtags’, I will add these two later on.