“Could not find the main class” when double-clicking .jar file

Question

First: I realize that this issue should be quite simple and lots of people seem to have experienced it. However, it appears my issue may be slightly different from

Answer 1

If the methods above cannot solve the problem, try deleting the .jar file type from your pc (you can google a software called Unassoc.exe and delete the file type), and then the problem is fixed! (At least, this is my case!)