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

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);