adding a key to HashMap without the value?

Question

Is there a way to add a key to a HashMap without also adding a value? I know it seems strange, but I have a HashMap> amd I wan

Answer 1

Yes, it was confusing enough ;) I don't get why you want to store keys without values instead just putting empty arraylists instead of null.

Adding null may be a problem, because if you call

map.get("somekey");

and receive a null, then you do not know, if the key is not found or if it is present but maps to null...