JDK 14 RF(pre)R: add section on "conditionally serializable" collections
Joe Darcy
joe.darcy at oracle.com
Sat Oct 5 00:02:16 UTC 2019
Hi Stuart,
I prefer your more extensive write-up and thus I review it to go back :-)
I've filed JDK-8231913: "Discuss serializability of collections" with
you as the assignee.
Thanks,
-Joe
On 10/4/2019 4:46 PM, Stuart Marks wrote:
>
>
> On 10/3/19 8:32 AM, Joe Darcy wrote:
>> In response to the recent and on-going review of serializable types
>> in the base module and elsewhere, I thought it would be helpful if
>> the collections specs discussed how collections were serialiazable.
>> In particular, the proposed terminology is that a collection is
>> "conditionally serializable" if the collection type implements
>> java.io.Serializable and all the elements of the collections are
>> serializable.
>>
>> Candidate wording changes to java.util.Collection below. If this
>> notion is deemed useful, I can also go through and add "This
>> collection is conditionally serializable."notes to ArrayList,
>> HashMap, and other such collections.
>
> Hi Joe,
>
> Thanks for doing this. In general I agree that there should be some
> discussion about the serializability of collections. I think it's
> reasonable to put that here (in the Collection interface) which seems
> to represent the top-level documentation for the entire Collections
> framework, not just that interface. I don't think it's necessary to
> mention conditional serializability in every location. However, I
> think a broader discussion of serializability in the collections
> framework is warranted. Here's some alternative wording:
>
>
> diff -r 4a98c87dfd89 -r 6aea42e7cb15
> src/java.base/share/classes/java/util/Collection.java
> --- a/src/java.base/share/classes/java/util/Collection.java Thu Oct
> 03 23:13:28 2019 -0700
> +++ b/src/java.base/share/classes/java/util/Collection.java Fri Oct
> 04 16:45:19 2019 -0700
> @@ -188,6 +188,38 @@
> * or if the only reference to the backing collection is through an
> * unmodifiable view, the view can be considered effectively immutable.
> *
> + * <h2><a id="serializable">Serializability of Collections</a></h2>
> + *
> + * <p>Serializability of collections is optional. As such, none of
> the collections
> + * interfaces are declared to implement the {@link
> java.io.Serializable} interface.
> + * However, serializability is regarded as being generally useful, so
> most collection
> + * implementations are serializable.
> +
> + * <p>The collection implementations that are public classes (such as
> {@code ArrayList}
> + * or {@code HashMap}) are declared to implement the {@code
> Serializable} interface if they
> + * are in fact serializable. Some collections implementations are not
> public classes,
> + * such as the <a href="unmodifiable">unmodifiable collections.</a>
> In such cases, the
> + * serializability of such collections is described in the
> specification of the method
> + * that creates them, or in some other suitable place. In cases where
> the serializability
> + * of a collection is not specified, there is no guarantee about the
> serializability of such
> + * collections. In particular, many <a href="view">view
> collections</a> are not serializable.
> + *
> + * <p>A collection implementation that implements the {@code
> Serializable} interface cannot
> + * be guaranteed to be serializable. The reason is that in general,
> collections
> + * contain elements of other types, and it is not possible to
> determine statically
> + * whether instances the element type are actually serializable. For
> example, consider
> + * a serializable {@code Collection<E>}, where {@code E} does not
> implement the
> + * {@code Serializable} interface. The collection may be
> serializable, if it contains only
> + * elements of some serializable subtype of {@code E}, or if it is
> empty. Collections are
> + * thus said to be <i>conditionally serializable,</i> as the
> serializability of the collection
> + * as a whole depends on whether the collection itself is
> serializable and on whether all
> + * contained elements are also serializable.
> + *
> + * <p>An additional case occurs with instances of {@link SortedSet}
> and {@link SortedMap}.
> + * These collections can be created with a {@link Comparator} that
> imposes an ordering on
> + * the set elements or map keys. Such a collection is serializable
> only if the provided
> + * {@code Comparator} is also serializable.
> + *
> * <p>This interface is a member of the
> * <a
> href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
> * Java Collections Framework</a>.
>
>
>
> s'marks
>
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