Having trouble finding direction in setting and resetting an ArrayList as a value in a HashMap

Question

I'm currently working on a simple program to add students and quiz scores to a HashMap. I'm able to add a student and his/her corresponding quiz scores but when adding scores, they are all the same as I'm reading every keys value as the same ArrayList. I'd like to be able to add 3 scores for each student, rather than every student having the same increasing list of scores. Just looking for some direction regarding this as I can't find a ton of info regarding ArrayList in a Hashmap. Maybe I'm just looking in the wrong place.

    UserIO inputReader = new UserIO();
    HashMap<String, ArrayList> students = new HashMap<>();
    ArrayList<Integer> quizScores = new ArrayList<>();

The UserIO class is just a simple input/output class. And here is my code for adding a student.

                //add a student
                String name = inputReader.readString("Please enter student name:");
                quizScores.add(inputReader.readInt("Enter score for quiz 1: ", 0, 100));
                quizScores.add(inputReader.readInt("Enter score for quiz 2: ", 0, 100));
                quizScores.add(inputReader.readInt("Enter score for quiz 3: ", 0, 100));
                students.put(name, quizScores);
                break;

Will I need to instantiate a new ArrayList for each individual student? Would a loop around my add code be helpful if that were the case?

Here is part of the prompt from the assignment:

The program must store student quiz data in a HashMap that has the student name as the key and an ArrayList of integers as the values. (Will this affect how you calculate average scores?)

Edit: an example of what I'm trying to stop from happening, after adding one student I get:

Mike [45, 67, 78]

and two students:

Mike [45, 67, 78, 45, 87, 68] Jim [45, 67, 78, 45, 87, 68]

*"Will I need to instantiate a new ArrayList for each individual student?"* Yes. — Andreas, Feb 15 '21 at 03:31

score 0 · Accepted Answer · answered Feb 15 '21 at 03:31

You are halfway there. You just need to add student scores correctly.

HashMap<String, List<>> students = new HashMap<>();

// Add quiz score addScore(studentId, score)
List<Integer> quizScores = students.get(studentId);
if (quizScores == null) {
    quizScores = new ArrayList<>();
}
quizScores.add(score);
// if data is not added by reference then set it back like below
students.put(studentId, quizScores);

Having trouble finding direction in setting and resetting an ArrayList as a value in a HashMap

1 Answers1