So I’m coding along and all of a sudden, Eclipse (3.4) can’t resolve classes. Classes that are in the same package as the class I’m editing. Classes that are fully qualified in the import statement.

Not good.

The last thing I had done was add a Spring @Autowired annotation. I saved the file and voila, everything goes to crap. I then spend a stupid amount of time trying to track down the cause. I took the changes out. I did a clean and rebuild and retest (everything passed; this was Eclipse-only). I added new classes to see if they broke (they did). I did a false modify (add space, remove space, save) to see if that broke said file (it did). It was a death spiral. No matter how I changed the code, the same problem was there.

Turns out, it wasn’t the annotation, or anything else in Spring, or any of my code, or any of my Eclipse plugins. It was a step before that killed me. I was doing a little cleanup and I created a temp directory at the top of my project folder so I could move some files there. It wasn’t nested in anything, other than the top level directory. What could go wrong?

Apparently, that makes Eclipse see red. Squiggly red.

The solution was simply to do a refresh (F5) on my project. Just as quickly as it started, the problem went away. That smells like a bug to me, but if it was I figure I’d see a lot more mentions in Google or the Eclipse bug tracker. I’m really hoping this helps someone save some time.

Update: If that doesn’t work, try:

Clean, refresh, build, restart

Also, remember any external build/clean scripts you might be using. For instance, Grails has a command line “clean” you may have to invoke. Same if you have Ant or Maven builds.

David Resnick (comment below) discovered this tip for those with an external build script:

Windows–>Preferences–>Java–>Compiler–>Building–>Output folder–>”Rebuild class files modified by others”.

This exists in Eclipse 3.5; I’m not sure about earlier versions.

Another issue I’ve found over the years is problems when upgrading Eclipse. In theory, new versions of Eclipse should update your workspace and project files just fine. In practice, they can become corrupted. My new rule is to create a new workspace for every major version upgrade of Eclipse (maybe more often if you’re cautious). Then I copy those projects and import the copy. This ensures I have a backup plan should something go awry. You may need to reimport your project(s) if there’s a problem that won’t go away after an upgrade.

Many commenters offered other solutions, so check below. Thanks to those who contributed them!

Update: I switched to IntelliJ. Click that link for details why, it’s not the usual hand-wavy “it’s just so much better” that never got me to switch. Not saying it’s bug free, but nothing is, and I’ve never seen errors like this there.

Keywords: false error, bogus error, eclipse bug