Proposal: ArrayList constructor perforrmance improvement

[Alan Bateman]

On 18/12/2018 16:44, Steve Groeger wrote:
> Hi all,
>
> I am proposing an enhancement to ArrayList.java to improve its
> performance.
>
> ArrayList has a constructor which takes an arbitrary Collection as a
> parameter. This constructor will create an iterator over the collection
> and it will add each entry returned to the ArrayList.
>
> We have found that quite a lot of the time the object passed as a
> parameter is in fact an instance of ArrayList.
> In the case of an ArrayList it is possible to significantly increase the
> performance of the method since there is no need for an iterator - the
> backing array can be directly copied.
>
ArrayList is not final so it's possible someone has extended it to use 
something other than elementData. It might be safer to use the class 
identity rather than instanceof.

-Alan