Question

Is it possible to keep multiple values corresponding to a key in a HashMap? If yes, how?

Answer 1

Yes, this is called chaining. You will want to avoid chaining as much as possible, especially if the size of the chain starts increasing. Longer chain size will counter the whole purpose of using a hash structure because the goal is to come as close to O(1) as possible.

Map<String, List<String>> hm = new HashMap<String, List<String>>();
List<String> values = new ArrayList<String>();
values.add("Value 1");
values.add("Value 2");
hm.put("Key1", values);