Intellij doesn't recognize class

Question

i was doing some homework in java but intellij doesn't recognize my class. It recognize the main class but it recognize the other class only on the first execution, whenever i modify the code and rebuild it intellij doesn't recognize the other class. I thought it was a jdk problem so i've downloaded an open source jdk but the problem persits. I've found no solutions yet, neither in the intellij forum. It sees the class only if i do a refactor but that's annoying. Mine intellij is up to date(7/5/19).

You can see in the pictures that intellij doesn't give me any problem on the syntax but it says that he cannot resolve "Matrix".

Answer 1

Running "File | Invalidate Caches" helped.

See manual.