By default on Windows Eclipse autocomplete shortcut is: Ctrl+Space. In my Mac laptop I use this combination for the operating system’s spotlight quick search. As a result, I wanted to change the default autocomplete shortcut. What you need to do is:
1. Go to Window->Preferences (Eclipse -> Preferences on Mac).
2. In the new window that pops up, go to “General -> Keys”
3. Find the “Content Assist” command and change it to whatever you like (in my case I chose Cmd+Space).
4. Don’t forget to click on “Save” on this pop up window!