How to use a variable of one class, in another in Java?

Question

I\'m just working through a few things as practice for an exam I have coming up, but one thing I cannot get my head round, is using a variable that belongs to one class, in

Answer 1

There should be 3 separate objects here, a Course, a Student, and an Enrollment. An enrollment connects a Student to a Course, a Course has many Students, and a Student can enroll in many courses. None of them should extend each other.