HashMap value change after "get"

Question

I have a

private Map<String,List<ProductScheme>> discountMap = new HashMap<String,List<ProductScheme>>();

now if i get list from discountMap and add an item in list will i have to put the list again in discount map or it will not be required ??

Answer 1

No it's not required. get returns a reference to the list stored in the map. So whatever modification you do on the list obtained with get (add, remove...) will be reflected on the list in the map too, because they are the same object.

Answer 2

You only need to add a List if it wasn't there before. A pattern I use is

List<ProductScheme> list = discountMap.get(key);
if (list == null)
    discountMap.put(key, list = new ArrayList<>());
list.add(value);