On Wed, 17 Feb 2021 14:21:37 GMT, Claes Redestad <redes...@openjdk.org> wrote:
>> src/java.base/share/classes/java/util/Collections.java line 1473:
>>
>>> 1471: public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ?
>>> extends V> m) {
>>> 1472: if(m.getClass() == UnmodifiableMap.class ||
>>> 1473: m.getClass() == ImmutableCollections.Map1.class ||
>>
>> (I'm not a reviewer.)
>>
>> I think this causes a change in behavior to this silly program.
>>
>> var map1 = Map.of(1, 2);
>> var map2 = Collections.unmodifiableMap(map1);
>>
>> try {
>> System.out.println("map1 returned " + map1.entrySet().contains(null));
>> } catch (NullPointerException e) {
>> System.out.println("map1 threw");
>> }
>>
>> try {
>> System.out.println("map2 returned " + map2.entrySet().contains(null));
>> } catch (NullPointerException e) {
>> System.out.println("map2 threw");
>> }
>>
>> With JDK 15 the output is:
>>> map1 threw
>>> map2 returned false
>>
>> With this change I think the output will be:
>>> map1 threw
>>> map2 threw
>>
>> It seems unlikely that anyone will be bit by this, but it is a change to
>> behavior and it wasn't called out in the Jira issue, so I felt it was worth
>> mentioning.
>>
>> I think it is just this one specific case that changes -- only `Map1`, and
>> only `entrySet().contains(null)`. Other sub-collections like `keySet()` and
>> `values()` and `subList(...)` already throw on `contains(null)` for both the
>> `ImmutableCollections.*` implementation and the `Collections.umodifiable*`
>> wrapper. `MapN`'s `entrySet().contains(null)` already returns `false` for
>> both.
>
> This sounds like an inconsistency between `Map1` and `MapN` that should
> perhaps be considered a bug that needs fixing. /ping @stuart-marks
2 remarks:
1. MapN's entry set extends abstract set, whose `contains` is null-friendly
like
https://github.com/openjdk/jdk/blob/cb84539d56209a6687c4ec71a61fdbe6f06a46ea/src/java.base/share/classes/java/util/AbstractCollection.java#L104
2. The problem of unmodifiable map's entry set not always delegating everything
to the backing entry set still exists.
https://github.com/openjdk/jdk/blob/cb84539d56209a6687c4ec71a61fdbe6f06a46ea/src/java.base/share/classes/java/util/Collections.java#L1724
This will bypass the underlying logic when the argument is `null` or not an
entry.
The behavior pointed out by michaelhixson is the conglomeration of these 2
unspecified behaviors.
-------------
PR: https://git.openjdk.java.net/jdk/pull/2596
