Convert Set to List without creating new List

Question

I am using this code to convert a Set to a List:

Map> mainMap = new HashMap<>();

for (int i         


        

Answer 1

You can use the List.addAll() method. It accepts a Collection as an argument, and your set is a Collection.

List mainList = new ArrayList();
mainList.addAll(set);

EDIT: as respond to the edit of the question.
It is easy to see that if you want to have a Map with Lists as values, in order to have k different values, you need to create k different lists.
Thus: You cannot avoid creating these lists at all, the lists will have to be created.

Possible work around:
Declare your Map as a Map or Map instead, and just insert your set.