How can list of values be changed insisde a map? (Java)

Question

I have this kind of map:

Map<String, List<String>> map = new HashMap<>();

And I'm trying to edit one of my list's values. This is how I tried to achieve that:

map.get(key).toArray()[index] = newString;

I convert my list into an array and assign new String. But this line of code does nothing. Is there any solution to it? I think I can just create a new list which will have a different value, but I hope there is a simpler way to achieve that.

Thank you in advance

Why are you converting the list into an array instead of just calling `put()` on it? — azurefrog, Mar 31 '20 at 16:42
What exactly do you wanna do ? each key has a list against against it, you want to update some values in the list right ? — Priyak Dey, Mar 31 '20 at 16:44
@azurefrog I tried to do that, but it requires me to put a new list. — dekanidze, Mar 31 '20 at 16:45
@azurefrog It looks like OP is trying to modify content of list, not map. `List` doesn't have `put` method, OP is most likely looking for `set(index, element)`. — Pshemo, Mar 31 '20 at 16:46

score 2 · Accepted Answer · answered Mar 31 '20 at 16:43

2

The List.toArray method creates an array that is a copy of the list. You can use the List.set method to set an item at an index

List<String> list = map.get(key);
list.set(index, newValue);

or, without a temporary variable:

map.get(key).set(index, newValue);

answered Mar 31 '20 at 16:43

Joni

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Yes, this is what I was trying to do! Thank you very much for a quick answer!:) – dekanidze Mar 31 '20 at 16:54

How can list of values be changed insisde a map? (Java)

1 Answers1