Question

How does a ArrayList react when one of the elements of a pair is entered as a null value?

My intent is to create a list for courses and the marks for those courses, but I’m wondering what happens if we don’t enter a score for a course. Would that throw an exception or just leave a null value at that element position?

Answer 1

Lists don’t have “pairs” – I think you mean Map, not List. Lists have single values, maps have pairs.

Maps can have null values for a given key.

Map<String, Integer> coursePoints = new HashMap<String, Integer>();
coursePoints.put("ABC001", 5);
coursePoints.put("XYZ002". null); // OK