Eclipse Error: The main class resolution process could not be found or could not be loaded

Yesterday in the MyEclipse, want to use a package to replace the existing package, the hand to delete the existing package, and then copy the new package, the entire package below the right corner of the file appears a deep red fork (not the kind of error form of the Red Fork), and then found to run a simple Java program are error, Said can not find or cannot load the main class, and then to the file directory to find, really did not produce class file, and then on Baidu search answers, Baidu found the following several solutions, I first listed:

1, environment variables are not configured well

I opened my environment variable confirmed two times and found no problem

2, right button, Properties->java Build path->libraries has a jar with a fork, remove off on the line

I looked at each other and found that there was no problem with the jar package.

3, on the src file right-click Build Path->use as Source Folder

And I this SRC is already source folder, even if I ordered the build Path->remove from build Path, and then use as Source folder is useless

Here is my solution, can be said to be simple and rude ...

I directly remove the project from the workspace, and then re-import, unexpectedly solved!

Eclipse Error: The main class resolution process could not be found or could not be loaded