RFR: 8180352: Add Stream.toList() method [v2]

[Peter Levart]

On 11/17/20 9:08 PM, Stuart Marks wrote:
> @plevart wrote:
>> Yes, but that is JDK16+ vs. JDK15- and not App V1 vs. App V2 thing. If both apps run on JDK16+, there will be no exception.
> Sure, the IMM_LIST_NULLS tag only helps with serialization compatibility across JDK releases.


I would say it goes the other way - it worsens the serialization 
compatibility. You are introducing a serialization format that is 
incompatible with older JDK releases. OTOH the problem of introducing 
nulls into List(s) in serializable data structures already exists 
because serializable List implementations that allow nulls already 
exist, so by introducing another one that is able to be deserialized on 
older JDK would not worsen the situation.


>   There are lots of ways an app can make incompatible changes to the serialized forms of its objects that we have no way of detecting.


So why bother with making the result of serialized stream.toList() not 
de-serializable on older JDK(s)? By making a favor to a hypothetical app 
that runs on older JDK and does not expect nulls in Lists of a data 
structure, you are also preventing an app that allows nulls in similar 
data structure from deserializing the datastructure on older JDK when 
the serialized form was produced with serializing stream.toList() on 
newer JDK.

But I see that the new  IMM_LIST_NULLS type is needed for one other 
thing - the immutable list implementation of that type has different 
behavior of indexOf and lastIndexOf methods (it doesn't throw NPE when 
null is passed to those methods) so this behavior has to be preserved in 
the deserialized instance and there is not way to achieve that on old 
JDK with existing serialization format, so there has to be an 
incompatible change in the serialization format for that matter.

Peter