Eclipse autocomplete not working in some Java files

Question

I have noticed that autocomplete is not working in some of java files in Eclipse. Also, the files where autocomplete is not working, display a hollow \"J\" as the icon for t

Answer 1

In this following picture, MyClass.java has a hollow J, because it is explicitly excluded from the sources to build:

Could you go to the properties of the project, "Java Build Path" Section, "Source" tab and see if some exclusion filter has been set ?
It is usual for instance to define:

**/Test*.java

to exclude at first building any unit-test class (when you have a large set of sources and do not want to be presented with Test classes during auto-completion, or do not want them considered during source searches).