Thanks everybody! This was a real tough one :) Maybe I'll ask Mark to put it on the Java 9 achievements slide at next JavaOne :)
On Wed, Feb 15, 2017 at 3:03 AM, David Holmes <david.hol...@oracle.com> wrote: > Looks good to me! > > Thanks, > David > > > On 15/02/2017 4:52 AM, Volker Simonis wrote: >> >> Hi, >> >> can I please have another review for the following trivial fix: >> >> http://cr.openjdk.java.net/~simonis/webrevs/2017/8174950/ >> https://bugs.openjdk.java.net/browse/JDK-8174950 >> >> This change has already been discussed in length on the mailing list: >> >> >> http://mail.openjdk.java.net/pipermail/core-libs-dev/2017-February/thread.html#46324 >> >> http://mail.openjdk.java.net/pipermail/core-libs-dev/2014-February/thread.html#24989 >> >> and in the bug comments at: >> >> https://bugs.openjdk.java.net/browse/JDK-8033909 >> >> So I'll give just (yet another) 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 >> >> Regards, >> Volker >> >
