RFR: JDK-8304933: BitSet (used for CSS pseudo class states) listener management is incorrect

[John Hendrikx]

On Mon, 10 Apr 2023 20:45:22 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> modules/javafx.graphics/src/main/java/com/sun/javafx/css/BitSet.java line 617:
>> 
>>> 615:     @Override
>>> 616:     public void removeListener(InvalidationListener invalidationListener) {
>>> 617:         if (invalidationListener != null) {
>> 
>> `Observable.removeListener(InvalidationListener)` is specified to reject `null` by throwing NPE.
>
> As with the earlier comment, any changes to the behavior of a null listener should be done separately and not part of this PR.

Alright, I'll file another ticket for that.  The general state of this class is quite poor, as it does not follow any of the contracts of the interfaces it implements (including `Collection`, `Set` and `ObservableSet`).  This is bad because even though this class is an implementation detail, it does get exposed as an `ObservableSet` via `Node#getPseudoClassStates`.  Things that it violates for example are:

     node.getPseudoClassStates().retainAll(null);   // no exception

Or:
   
     node.getPseudoClassStates().retainAll(set2);   // does nothing if set2 is not a BitSet

Or:

     // fails, even if they're the same because `equals` assumes another BitSet     
    node.getPseudoClassStates().equals(Set.of(PseudoClass.getPseudoClass("armed"));

     // works:
     Set.of(PseudoClass.getPseudoClass("armed")).equals(node.getPseudoClassStates());

Same goes for the hash code value; these are strictly defined for sets, but `BitSet` violates it causing problems when using these sets as keys.  This causes numerous odd problems that I had to track down while implementing #1076 -- I can only assume very few people are using these API's in the wild.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1071#discussion_r1162126275