Updating an entry of a HashMap whose values is a List

User_67128 :

I have a HashMap<Integer, List<Integer>> "sq_diff" and I am trying to update an entry.

I tried:

List<Integer> values = sq_diff.get(diff);
values.add(c);
values.add(d);
sq_diff.put(diff, values);

and

sq_diff.get(diff).add(c);
sq_diff.get(diff).add(d);

and

sq_diff.computeIfPresent(diff, (k, v) -> v.add(c);
sq_diff.computeIfPresent(diff, (k, v) -> v.add(d);

None of them working:

Exception in thread "main" java.lang.UnsupportedOperationException

The map contains an entry of "diff"

Highly appreciated if you can indicate problems on each of them.

abhimanyue :

Try this,

List<Integer> values = new ArrayList<>(Arrays.asList(c, d));
sq_diff.put(diff, values);

instead of

sq_diff.put(diff, Arrays.asList(c, d));

Origin http://10.200.1.11:23101/article/api/json?id=419054&siteId=1

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