Solution when java completion candidate does not appear after updating to eclipse 2018-12
- Remove any content_assist_disabled_computers settings in the files in .metadata / .plugins / org.eclipse.core.runtime / .settings
- Java → Editor → ContentAssist → Advanced Java Non-Type Proposals, Java Proposals, Java Type Proposals If not checked, enter
- Delete the .index file extension in .metadata / .plugins / org.eclipse.jdt.core