Eclipse error “Could not find or load main class”

Question

I know there are many duplicates of this question, but I have looked at them all, and none of them have solved the issue.

I am trying to run a class that has a main

Answer 1

I followed several of the less drastic suggestion here to no avail. Then it dawned on me that Eclipse was confused because I had made a backup copy of my src project folder. (It was compiling all these "copy of" folders' *.java files and I noticed the subfolders for them in my bin folder.) I moved the backup elsewhere, got rid of the extraneous class files, did a Project > Clean, and everything was back to normal.