Convert Set to List without creating new List
Use constructor to convert it:
List<?> list = new ArrayList<>(set);
You can use the List.addAll() method. It accepts a Collection as an argument, and your set is a Collection.
List<String> mainList = new ArrayList<String>();
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 List
s 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<String,Set>
or Map<String,Collection>
instead, and just insert your set.