Eclipse type hierarchy not always working

Question

When I want to see implementation of some interface through F4 (type hierarchy) or ctrl+t (quick hierarchy) or implementation of a method, I

Answer 1

I had this same problem and fixed it by deleting the Eclipse index cache files located in .metadata/.plugins/org.eclipse.jdt.core. Delete all .index files and savedIndexNames.txt. Do this while Eclipse is not running and then restart. This fixed the issue for me.