RFR: 8318420 : AbstractPipeline invokes overridden method in constructor

[Paul Sandoz]

On Wed, 18 Oct 2023 09:45:53 GMT, Viktor Klang <vklang at openjdk.org> wrote:

> This PR corrects so that `opIsStateful()` is not invoked as a part of the java.util.stream.AbstractPipeline constructor—as `opIsStateful()` is intended to be overridden by subclasses, and as their own constructors have not run when their superclass constructor runs, this means that `opIsStateful()` cannot base its return value on any class members of the subclass.
> 
> Since `opIsStateful()` is only needed for parallel streams, we can therefor defer the invocation of `opIsStateful()` until evaluation-time, and as such we can remove the need for having an instance field to store the result of the invocation—making Stream instances potentially a tiny bit smaller, reducing Stream-construction overhead, while still preserving semantics.

Marked as reviewed by psandoz (Reviewer).

-------------

PR Review: https://git.openjdk.org/jdk/pull/16239#pullrequestreview-1685991329