Navigate to Window -> Preferences -> General -> Keys. Find Content Assist. Delete Ctrl+Space from the binding field, and hold down Ctrl and press space:
- If only Ctrl+ is displayed, then something is intercepting the Ctrl+Space key binding before it reaches Eclipse. For me, it was IBus (in XFCE, go to Settings -> Input Method Selector, Use IBus -> Preferences*, and check the Enable or disable keyboard shortcut. If it's set to Ctrl+Space, clear the field, click Apply, and restart Eclipse).
- On the other hand, if Ctrl+Space is displayed, then Eclipse is able to receive the key combination. Go to Window -> Preferences -> Java -> Editor -> Content Assist -> Advanced and make sure all relevant proposals are enabled. Other than that, just ensure dodgy import statements aren't affecting content assist's ability to recommend completions.
* Update: under Xubuntu 12.10, this seems to be slightly different, and Preferences is no longer available in this dialog. No matter; fire up a terminal and start
ibus-setup. Delete Ctrl+Space from the keyboard shortcuts. There was no need to restart Eclipse.
