Why auto-boxing marked as a warning?

Question

I understand that auto un-boxing should be done with care because the reference that is being un-boxed can be null. Why is auto-boxing marked as warning as well? Are there some

Answer 1

Autoboxing can contribute to the developer creating a bug related to the "remove" method of Collections, though this is probably a pretty obscure bug.

I've encountered this bug when I used a random number generator to select the index of an item to remove from an ArrayList. The generator returned a long primitive, which I accidentally tried to use as the parameter for List.remove(int index). The compiler converted the long to a Long and used it in List.remove(Object o), which gave totally different behavior. Luckily, an assert statement caught the error quickly.

According to this discussion of this issue with "remove", someone else ran into a similar problem where their int unexpectedly acted like an Integer, though I don't understand how that happened. Why aren't Java Collections remove methods generic? (see comment by ScArcher2)