intellij doesnt compile some classes that are in the source folder

Question

I tried to use some methods in a class. When I tried to use them it can't find the class in the source folder. the source folder and the code

The class is right there in the source folder, and the line and point classes can be used just fine. Why won't GUI and DrawSurface work?

I also tried it like this: the classes in a folder and I import them like you can see there are a lot of classes in there, but when I want to import one of them it doesn't work.

Answer 1

I think, you should choose JDK

File -> Project Structure -> Project -> Project SDK

Answer 2

Why do you keep compiled classes in sources folder? Move them to separate folder and add it as dependency in "Project Structure | Modules | Dependencies"