Are there any exams for public elective courses in universities? Is it difficult if you take the exam?

You need an exam, but generally it is not necessarily a written one. You can also take exams by handing in reports or other exams. This is basically decided by the teacher. Some teachers will easily pass the experience or report, and some teachers will fail many written tests if they are serious. Of course, they are definitely much looser than the general compulsory courses.