intellij has placed what look like no entry signs over my java files (red circles with a line through) searched around but cannot find why? Would anyone know please.
It\
It means those files aren't part of the project settings. How did you create that project?
I'm not sure which version of IntelliJ you're using - I run 9.0.1. I'd recommend opening the project structure (icon to the right of the "wrench" or Ctrl+Alt+Shift+S), click on "Modules", and designate the directory where the .java files are located as a source directory (it'll change to a blue color).
For those who have this problem with Android Studio. Try the following:
1) Navigate to your project settings
2) Go to Modules -> and under the module option tab select "Sources" - There should be an option to "Add Content Root" and below it, blue, green, and red tab folders for Source Folders, Test Source Folders, and Excluded Folders respectively.
3) On the right side, right click on the java source folder you want to add and select to add it to Source or Tests (depending on what kind of files you are adding).
4) The added files should now show up with a blue circle with a c in the center on the left hand project window pane.
For maven projects:
In my case I had to import the project through Maven. Some modules were missing (they weren't specified in the root pom) so adding those as maven projects fixed the issue.
click on the 'plus' icon on the right hand side maven menu and then add the project. This imported all sources / structure automatically.