Eclipse doesn't compile java files into classes

open problems view from window -> show view -> problems, if there's any error, fix it

eclipse will reject to compile if there is any problems in your project

Close Project -> Open Project -> Clean -> Refresh

Hope it helps for someone else

This problem happens when "for some reasons" your project is corrupted and has a red icon near the project's name in Eclipse. The solution is to save the project's folder, delete the project in Eclipse, than create the project again in Eclipse coping all the previous files saved.