There is very important shortcut for Basic Code Completion in IntelliJ IDE which assumed to be invoked as ctrl+space shortcut on Mac. The problem is this shortcut is system one and used to invoke "Spotlight" in Lion Mac OS. How you guys invoke it then?
You either disable/change Spotlight shortcut in the system settings or you change the Basic completion shortcut in IDEA Preferences | Keymap.
I think that the question is motley asking to what key combination do you change it, and why JetBrains haven’t implemented the update to the mac keymap by themselves.
Anyways, I’ve swapped the Ctrl+Space with Alt+Space which doesn’t seem to collide with any MacOSX system key shortcut.
You can override the OSX spotlight shortcut in IntelliJ IDEA/Services/Services Preferences. More info: here.
I dont know if this helps but here is a list of the default key mappings http://www.jetbrains.com/idea/docs/IntelliJIDEA_ReferenceCard_Mac.pdf and you can change them from the menu IDE Settings -> Keymap
Alternatively, you can use Ctrl + Shift + Space for "SmartType" to avoid collision with Spotlight.
Actually, spotlight is started by COMMAND-space and not by CTRL-space ...
来源：https://stackoverflow.com/questions/11085913/basic-code-completion-in-intellij-on-mac