RFR: 8264770: BidirectionalBinding should use InvalidationListener to prevent boxing

[Kevin Rushforth]

On Sat, 3 Apr 2021 15:20:41 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

> The internal BidirectionalBinding class implements bidirectional bindings for JavaFX properties. The design intent of this class is to provide specializations for primitive value types to prevent boxing conversions (cf. specializations of the Property class with a similar design intent).
> 
> However, the primitive BidirectionalBinding implementations do not meet the design goal of preventing boxing conversions, because they implement ChangeListener.
> 
> ChangeListener is a generic SAM interface, which makes it impossibe to invoke an implementation of ChangeListener::changed with a primitive value (i.e. any primitive value will be auto-boxed).
> 
> The boxing conversion happens, as with all ChangeListeners, at the invocation site (for example, in ExpressionHelper). Since the boxing conversion has already happened by the time any of the BidirectionalBinding implementations is invoked, there's no point in using primitive specializations of BidirectionalBinding after the fact.
> 
> This issue can be solved by having BidirectionalBinding implement InvalidationListener instead, which by itself does not incur a boxing conversion. Because bidirectional bindings are eagerly evaluated, the observable behavior remains the same.
> 
> I've filed a bug report with the same title.

The fix looks good, but I noted two places where I think you need to initialize `oldValue`.

modules/javafx.base/src/main/java/com/sun/javafx/binding/BidirectionalBinding.java line 585:

> 583:         private TypedGenericBidirectionalBinding(Property<T> property1, Property<T> property2) {
> 584:             super(property1, property2);
> 585:             propertyRef1 = new WeakReference<>(property1);

Don't you need to initialize `oldValue` here?


    oldValue = property1.get();

modules/javafx.base/src/main/java/com/sun/javafx/binding/BidirectionalBinding.java line 657:

> 655:         private TypedNumberBidirectionalBinding(Property<T> property1, Property<Number> property2) {
> 656:             super(property1, property2);
> 657:             propertyRef1 = new WeakReference<>(property1);

Same comment as above. Shouldn't `oldValue` be set?

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

PR: https://git.openjdk.java.net/jfx/pull/454