PROPOSAL : Specify nullable argument

[Jeremy Manson]

I don't know what the current state of the 305 proposal is, but Bill
has been talking about at least three annotations in informal
conversations.

Jeremy

On Tue, Mar 17, 2009 at 5:27 PM, Reinier Zwitserloot
<reinier at zwitserloot.com> wrote:
> Adding non-nullity to the type system would be a great boon, IMO, but
> its far more complicated than just having a @NonNull annotation.
>
> I've written up a proposal a while ago here: http://www.zwitserloot.com/2008/10/23/non-null-in-static-languages/
>
> Suffice to say it gets very complicated because you need 4 nullity
> states (Never-Allows-Null, Definitely-Allows-Null, Might-Allow-Null,
> Legacy (like raw generics, for interop with old code), *AND* you need
> a separate process to promote or demote generics (So that you can say:
> Eventhough this is a Map that maps NonNull String to NonNull String,
> if you call get() on this, you get a @Nullable String back, because
> null will flow out if I can't find the key. In other words, the 'V'
> generics parameter needs to be demoted to @Nullable V somehow).
>
> Read the blog entry for a more elaborate explanation with examples.
>
> I'd love something like that in java, but the proposal as it stands
> needs a source 1.7; keyword (because having no modifier is taken as
> 'never null', which is obviously not backwards compatible), and is
> very complicated, so: Definitely not project coin material.
>
> Incidentally, I think jsr305 is fundamentally broken. It doesn't have
> the states needed to convey nullity info; it needs at least 2
> annotations, probably 3 to be able to differentiate between code that
> simply didn't specify anything, and code that did, instead of the one
> annotation that jsr305 gives.
>
>  --Reinier Zwitserloot
>
>
>
> On Mar 17, 2009, at 21:41, Neal Gafter wrote:
>
>> Did you intend this to be a complete proposal?
>>
>> Do you like this better than @NonNull, which will probably be included
>> in Java 7 under jsr 305?
>>
>> On Tue, Mar 17, 2009 at 1:25 PM, Olivier Chorier
>> <lapsus63 at gmail.com> wrote:
>>> Example :
>>>
>>> public void getListOfProducts(Company owner, !String facultativeName)
>>> {
>>> ....
>>> }
>>>
>>> The '!' should prevent the developper that the argument is able to
>>> be null.
>>> Invoking getListOfProducts(null, "name") could throw a compilation
>>> error/warning.
>>>
>>> Or maybe better :
>>>
>>> public void getListOfProducts(!Company owner, String facultativeName)
>>> {
>>> ....
>>> }
>>>
>>> Here, the '!' indicates a mandatory argument (not null).
>>>
>>>
>>> However, I don't know if the '!' marker could be the most
>>> appropriate.
>>>
>>>
>>
>
>
>