These bugs (and a solution if you use Eclipse >3.4) may be of interest to you:
A. Allow more character triggers as @Samuel said (fixed in 3.4 onwards):
https://bugs.eclipse.org/bugs/show_bug.cgi?id=159157
Change the default in Auto activation triggers for Java to ._abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
B. Allow content assist everywhere automatically (not fixed):