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

Jeff Dinkins jeff.dinkins at oracle.com
Thu Feb 9 16:32:56 UTC 2017

Adding Mike’s current email.


> 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 :)

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