使用java中的方法验证课程代码

I have to get my course code to validate. The course code is set to a number 1-7 and the choice has to be within this range. Each course is worth 3 credits. The user can not register for more than 9 credits. The user can not register for the same course more than once. I am having trouble with the repeat course code.I have to get my course code to validate. The c