RFR(XS): 8033909: Objects.requireNonNull(T, Supplier) doesn't specify what happens if the passed supplier is null itself

[David Holmes]

FWIW I think a null Supplier should simply be ignored.

David

On 13/02/2017 6:04 PM, Volker Simonis wrote:
> Ping...
>
> On Thu, Feb 9, 2017 at 5:32 PM, Jeff Dinkins <jeff.dinkins at oracle.com> wrote:
>>
>> Adding Mike’s current email.
>>
>> -jeff
>>
>>> On Feb 9, 2017, at 10:18 AM, Volker Simonis <volker.simonis at gmail.com> wrote:
>>>
>>> Hi,
>>>
>>> I want to finally resolve this long standing issue (or close it as
>>> "will not fix" if that's not possible):
>>>
>>> http://cr.openjdk.java.net/~simonis/webrevs/2017/8033909/
>>>
>>> This change has already been discussed in length on the mailing list:
>>>
>>> http://mail.openjdk.java.net/pipermail/core-libs-dev/2014-February/thread.html#24989
>>>
>>> and in the bug comments:
>>>
>>> https://bugs.openjdk.java.net/browse/JDK-8033909
>>>
>>> So I'll give just a short summary here:
>>>
>>> - Objects.requireNonNull(T, Supplier) does not check for the Supplier
>>> argument being null. Instead it relies on the fact, that the VM will
>>> implicitly throw a NullPointerException when it calls .get on the
>>> Supplier argument during the creation of the explicit
>>> NullPointerException which it is supposed to throw.
>>>
>>> - this behavior slightly differs from Objects.requireNonNull(T,
>>> String) which simply creates a NullPointerException with a null
>>> message in the case where the String argument is null.
>>>
>>> - the difference is not evident in the OpenJDK, because the HotSpot VM
>>> creates a NPE with a null message by default if we call a method on a
>>> null object.
>>>
>>> - however creating such a NPE with a null message when invoking a
>>> method on a null object is not enforced by the standard, and other
>>> implementations can do better :) For the following trivial program:
>>>
>>> public class NonNull {
>>>  public static void main(String[] args) {
>>>    Supplier<String> ss = null;
>>>    Object o = Objects.requireNonNull(null, ss);
>>>  }
>>> }
>>>
>>> the current OpenJDK implementation returns:
>>>
>>> Exception in thread "main" java.lang.NullPointerException
>>>    at java.util.Objects.requireNonNull(Objects.java:290)
>>>    at NonNull.main(NonNull.java:8)
>>>
>>> but the SAP JVM will print:
>>>
>>> Exception in thread "main" java.lang.NullPointerException: while
>>> trying to invoke the method java.util.function.Supplier.get() of a
>>> null object loaded from local variable 'messageSupplier'
>>>    at java.util.Objects.requireNonNull(Objects.java:290)
>>>    at NonNull.main(NonNull.java:8)
>>>
>>> which is at least confusing for a call to Objects.requireNonNul() with
>>> a null Supplier. We think the exception should be the same like the
>>> one we get when invoking Objects.requireNonNul() with a null String.
>>>
>>> - because of this difference (and because we like our extended
>>> Exception messages :) the JCK test for Objects.requireNonNul(T,
>>> Supplier) (i.e.
>>> api/java_util/Objects/index.html#RequireNonNullMessageSupplier) was
>>> removed from TCK 8 and is still commented out in TCK 9
>>> (npe_checkingNullSupplier() in RequireNonNullMessageSupplier.java).
>>>
>>> I really think that the simplest and most natural fix for this problem
>>> is to simply check for a null Supplier argument and create the NPE
>>> with an explicit null message in that case (as outlined in the
>>> webrev). This:
>>> - makes the two requireNonNul() overloads for String and Supplier
>>> behave the same (which I think was the initial intention).
>>> - doesn't require documentation changes
>>> - makes it possible to write a simple and conforming TCK test
>>>
>>> If we can't agree on this quickly, I suggest to close the issue as
>>> "will-not-fix" and leave it untested by the TCK.
>>>
>>> Thank you and best regards,
>>> Volker
>>>
>>> PS: the 'XS' obviously only applies to the fix, not to this message :)
>>