RFR: 8196586: Remove use of deprecated finalize methods from javafx property objects

[Nir Lisker]

On Tue, 18 Feb 2020 20:09:59 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>>> the referent to the created property object has been garbage collected before the `finalize` method is called
>> 
>> I'm confused. What is that referent exactly and why is it guaranteed to have been GC'd before finalization?
> 
>> > the referent to the created property object has been garbage collected before the `finalize` method is called
>> 
>> I'm confused. What is that referent exactly and why is it guaranteed to have been GC'd before finalization?
> 
> I meant the referent of the `WeakReference` to the constructed `Property` object on which the `finalize` method is being called.
> 
> The `asObject` and `xxxxxProperty` methods create a bidirectional binding, which uses weak references to both the original `Property` object and the newly constructed `Property` object. The `finalize` method is on the newly-constructed `Property`. By the time that finalize method is called, the JVM guarantees that no other reference to that  `Property` object exists. From the API docs of `Object::finalize`:
> 
> _The general contract of finalize is that it is invoked if and when the Java™ virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized._

The logic seems correct. The weak reference to the newly created property in the bidirectional binding must be cleared before `finalize` is called. The unbinding attempt only interferes with GC.

I still have to go over the tests.

I note that with the removal of the finalize methods, the method `BidirectionalBinding#unbindNumber` is left unused and can be removed.
Also, the changed property classes and `BidirectionalBinding` can use some cleanup that I can do after this is fixed, so I can remove that method at that time if you don't want to do it here.

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PR: https://git.openjdk.java.net/jfx/pull/113