I had that same problem happen to me before too. The cause of it was that my project was imported as a Maven project and not as a Java project. So maybe converting the project back to java type could help.
If it's not that, then try this:
1. type a period in eclipse so that the error will appear then click on "Content assist."
2. Click on Content Assist Settings, then on "Auto activation triggers for Java"; delete the period, then click apply to save.
Hope this helps!