發現下面的解法,原來被uncheck了 Bug 222403 – [code assist] no proposals after uninstalling Mylyn : "This is a known Mylyn bug: they tweak the preferences and once this workspace is moved on to a new build without Mylyn you can end up with this. 1. go to the following preference page: Java > Editor > Content Assist > Advanced 2. click 'Restore Defaults' 3. click 'OK' This should fix your problem."