On Fri, 14 May 2021 22:30:16 GMT, Michael Strauß <mstra...@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.
>
> Michael Strauß has updated the pull request incrementally with one additional
> commit since the last revision:
>
> added missing oldValue assignments
modules/javafx.base/src/main/java/com/sun/javafx/binding/BidirectionalBinding.java
line 157:
> 155:
> 156: property1.setValue((T)property2.getValue());
> 157: property1.addListener(binding);
About lines 156-158:
property1.setValue(property2.getValue());
property1.addListener(binding);
property2.addListener(binding);
The bindings added do not validate the properties anymore as it is an
invalidation listener now instead of a change listener. This doesn't matter
for `property2` as its `getValue` is called which will force its revalidation,
but for `property1` this is not the case. This small program demonstrates this:
SimpleDoubleProperty p = new SimpleDoubleProperty(2);
InvalidationListener invalidationListener = obs ->
System.out.println("Invalidated");
p.addListener(invalidationListener);
p.setValue(3);
p.setValue(4);
The program as expected only prints `invalidated` once.
-------------
PR: https://git.openjdk.java.net/jfx/pull/454
