There is a problem with the program you have written to date. Every year there are students with different names, but end up with the same userID. This is a problem, each user must have a unique userID name.
You need to decide on a strategy to find these duplicate userIDs and output them to a second file.
Do NOT start programming until you have talked to me about the strategy you are going to use.
You may use the Internet to help you with ideas for your strategy.
You may find Java: ArrayList Sort helpful