Nulls

[Doug Lea]

On 09/25/12 10:48, Brian Goetz wrote:
> null-aware as much as simply null-inappropriate -- i.e., don't use this method
> if you have nulls in your streams -- which means that the user does has to be
> null-aware.  Which I think is your point -- the user has to reason about it.

Yes. If the base framework kicks the nullness problem to its users,
then every user must deal with it. But many of the "users" of java.util
are not applications programs, but other utilities and frameworks that
do not know whether the issues apply or not.

>>    boolean present;
>>    T x;
>>    try {
>>         Optional<T> r = ...findAny(...);
>>         if (present = r.isPresent()) x = r.get();
>>    } catch(NPE ex) {
>>        present = true;
>>        x = null;
>>    }
>>
>> Not very nice.
>
> Or more nice:
>
>     ....filter(o -> o != null).findAny();

No. If this is part of a utility as opposed to application program,
then it doesn't know if nulls are allowed or not, so has to be
correct in either case; or else advertise its policy as an
unchecked precondition. Many people will not do either of these.
This is the where most of the mistakes will appear.
So in the likely event that you choose these rules anyway,
it would be nice to at least alert the bug-detector folks
to look for such constructions.


-Doug