RFR: 8214699: Node.getPseudoClassStates must return the same instance on every call

[Kevin Rushforth]

On Thu, 18 Jun 2020 16:30:42 GMT, Ambarish Rapte <arapte at openjdk.org> wrote:

> Node.getPseudoClassStates() returns a new UnmodifiableObservableSet of PseudoClassState on each call. So in order to
> listen to any changes in this set, user must call the method Node.getPseudoClassStates() only once and keep a strong
> reference to the returned UnmodifiableObservableSet.
>  
> So the fix is that the method Node.getPseudoClassStates() should return the same UnmodifiableObservableSet on every
> call. As the returned set is an UnmodifiableObservableSet, it will not have any impact on it's usage.
>  
> Added a small unit test. and,
> Altered(minor) a test which was modified in
> past(https://github.com/openjdk/jfx/commit/0ac98695a1b11443c342fad4f009d6e03a052522)
> (https://github.com/openjdk/jfx/commit/62323e0a9c5817b33daa262d6914eba0e8d274ff) along with this method and should be
> updated in view of this change.

The fix looks good, given that `FXCollections.unmodifiableObservableSet()` wraps an observable set listens to changes
to the backing set. Can you add a test to ensure that the listeners are getting called?

modules/javafx.graphics/src/test/java/test/javafx/scene/NodeTest.java line 168:

> 167:         assertSame("getPseudoClassStates() should always return the same instance",
> 168:                 node.getPseudoClassStates(), node.getPseudoClassStates());
> 169:     }

To make this more clear, I recommend to store the expected value in a local variable and then call assert.

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

PR: https://git.openjdk.java.net/jfx/pull/253