Help with program

Question

I have attached a zip to the post and I need help trying to finish this. The problems I am having are when I click the nextStudentButton and laststudentbutton it goes until the end of the array. I would like to get it to stop at the last name that is stored in the arraylist.  Then i also am having trouble when i am adding a student to the arrayList I want to be able to compare the idnumber of the student already in the list to the id number of the new student I am adding and if the any two id numbers are the same then the student cannot be added. Any help would be appreciated. Thanks