ArrayDeque and List

[Martin Buchholz]

https://openjdk.markmail.org/search/?q=8143850#query:8143850%20list%3Anet.java.openjdk.core-libs-dev+page:1+state:facets

On Sat, Jun 30, 2018 at 12:53 PM, Jonas Konrad <me at yawk.at> wrote:

> Hey,
>
> The introduction of ArrayDeque in Java 1.6 has basically replaced
> LinkedList as the "default" implementation of java.util.Queue, which is
> probably for the best. However, from time to time, I still see use cases
> where a class that implements both Deque and List is wanted for ease of
> use. LinkedList is currently the only class that supports this. One example
> would be sorting the queue in-place.
>
> Has there been any discussion on having ArrayDeque implement List?
>
> There is no *technical* reason against doing so - the internal structure
> of ArrayDeque is fully capable of supporting an implementation of List, and
> there would be no additional fields needed that would change current memory
> behavior. The existing Deque interface would also remain unaffected.
>
> I see two possible reasons against doing this:
>
> - Added maintenance effort, a lot of it duplicated from ArrayList. This
> *could* be done gradually: ArrayDeque only extends AbstractCollection right
> now so implementations for e.g. subList could be inherited from
> AbstractList. Performance tweaking would be nice in many places though.
> - Design - conceptually, a Deque is something very different from a List.
> LinkedList implementing both could be seen as a mistake from that point of
> view. When coding to interfaces, which is good practice anyway, this change
> isn't visible though.
>
> Thoughts?
>
> - Jonas Konrad
>