How to convert a List to Set in Java? ArrayList to HashSet Example

Converting ArrayList to Set in Java means creating a Set implementation like HashSet from an ArrayList full of objects. Before Converting your ArrayList into HashSet do remember that List keeps insertion order and guarantees the same but Set doesn't have such obligation. Also, List allows duplicates but Set doesn't allow any duplicates, which means if you have duplicates in your ArrayList they will be lost when you convert ArrayList to HashSet and that's the reason why the sometimes size of ArrayList doesn't match with the size of HashSet after conversion.