JEP 269: Convenience Factory Methods for Collections

Kevin Bourrillion kevinb at
Fri Oct 2 16:22:00 UTC 2015


On Fri, Sep 25, 2015 at 12:20 PM, Remi Forax <forax at> wrote:

> Note that without permitting nulls, Map.of(key, Optional.of(value)) will
> > become reasonably common, and that fact you can't serialize that will
> > become even more strange than it already is.
> Please don't do that, if you have a mapping between a key and something
> that doesn't exist, the best is to not have that mapping,
> this is the semantics of java.util.concurrent (with null instead of
> Optional) and this is the only sane semantics.
> Optional should never appear in collections/maps, it makes the code that
> deal with this kind of beast stupidly harder to read/write for no benefit.

If you had no need to distinguish between not-present and mapped-to-absent,
then the idea of using a Map<K, Optional<V>> is so bizarre that I'm not
sure why we would even discuss it.

We have ~1800 occurrences of Optional-valued Maps or Caches in Google. They
do this for an actual reason: a negative result is meaningfully different
from no result. This is addressed in our Optional javadoc

Kevin Bourrillion | Java Librarian | Google, Inc. | kevinb at

More information about the core-libs-dev mailing list