I've done some searching with Google using this query:
"javafx.collections.ObservableMap" "implements ObservableMap"
And found what I think are only two distinct pieces of code that
implements ObservableMap (aside from the ones in JavaFX).
One is in the Griffon framework which still seems to be an active
project. See these files:
https://github.com/griffon/griffon/blob/development_3_X/subprojects/griffon-javafx/src/main/java/griffon/javafx/collections/transformation/TransformationMap.java
https://github.com/griffon/griffon/blob/development_3_X/subprojects/griffon-javafx/src/main/java/griffon/javafx/collections/ObservableMapBase.java
The ObservableMapBase is declared as:
public abstract class ObservableMapBase<K, V> extends
AbstractMap<K, V> implements ObservableMap<K, V>
Aside from Griffon framework, there is another use in a `SharedKeysMap`:
public class SharedKeysMap<K, V> extends AbstractMap<K, V>
implements ObservableMap<K, V> {
It's described as a map which stores its values in an array and which
can share its keys with other `SharedKeysMap`s. I can't find anything
about where this might be used, so it's probably a personal project.
That said, it doesn't look like this occurs in any of the more popular
frameworks used with JavaFX. I'm not sure about Griffon's popularity
(first I heard of it). It's actively developed so if there is a
migration path we might be able to contribute a solution. I also
checked more directly code in ControlsFX, ReactFX, RichTextFX and JFXtras.
--John
On 28/10/2022 23:56, Stuart Marks wrote:
Hi,
I'm impressed you found that compatibility report. :-)
The most severe compatibility issues indeed occur if the keySet(),
values(), and entrySet() methods are overridden to have a covariant
return type. Issues will arise with subclasses that already override
any of those methods, either with the return types from Map, or with
covariant overrides of their own.
It's true that bridge methods will be generated if this is done, and
they take care of the most common compatibility issues. However, there
is a compatibility matrix to be explored. My compatibility analysis
considered old-binary, recompiled-source, and modified-source cases
for both a library that has an at-risk subclass as well as an
application that uses that library subclass. Some startling things
emerged. What pushed me over the edge to decide against covariant
overrides (in this part of the Sequenced Collections JEP) was that the
behavior of a class could change silently upon recompilation, even if
the source code wasn't changed.
Aside from this issue, there's a more fundamental semantic issue with
the object design. If I have some ObservableMap implementation,
presumably it provides a keySet() implementation that's not
observable. If ObservableMap is changed to have the covariant
overrides, this effectively imposes a new requirement that existing
implementations cannot possibly fulfill. Sure, you could tinker things
around so that things appear to work in some cases, but the semantics
of doing this are highly questionable.
Now JavaFX could decide go ahead with this anyway, for a couple
reasons. One might be, JavaFX doesn't care as much as the JDK about
compatibility. It's (mostly) a different project, and it might have
different compatibility constraints. You folks need to decide that. A
second reason might be because there are vanishingly few or zero
implementations of ObservableMap "in the wild," so any incompatibility
would not cause any actual problems. This is difficult, but it's
possible to get some information by doing source code searches.
(Unfortunately there appear to be several libraries out there that
have something called "ObservableMap" which will complicate the analysis.)
The alternative is to add observableKeySet/Values/EntrySet() default
methods instead of covariant overrides. This is safer, but it does add
some clutter to the API.
s'marks
On 10/26/22 1:24 PM, Nir Lisker wrote:
I'm CC'ing Stuart Marks who has recently dealt with a similar issue
when working on Sequenced Collections [1], and wrote a compatibility
report [2] that includes an item about covariant overrides
("Covariant Overrides of `SequencedMap` View Collection Methods"),
which is similar to what is discussed here. I contacted him off list
to get his insights into the risks involved here.
To recap, ObservableMap inherits keySet(), entrySet() and values()
from Map, which return the standard Set and Collection interfaces.
ObservableMap should provide ObservableSet and perhaps the
not-yet-existing ObservableCollection. There are 2 options here: one
is to add additional default methods to ObservableMap that return
observable collection, the second is to override the methods
inherited from Map and change the return value. The latter has some
backwards compatibility issues. It comes down to implementations of
ObservableMap in the wild. I have yet to see any, personally. JavaFX
does not itself expose any of its implementations, as ObservableMaps
are obtained through FXCollections static methods.
I'd like to continue this discussion about the API side. I have
already had some advances on the implementation.
[1] https://openjdk.org/jeps/431
[2] https://bugs.openjdk.org/browse/JDK-8266572
On Tue, May 31, 2022 at 12:02 AM Nir Lisker <[email protected]> wrote:
Then maybe a solution would be around adding new methods like
observableKeySet(). These will need to be default methods, and
the implementation could test if keySet() already returns an
ObservableSet, in which case it returns it, and if not it wraps
the Set in an ObservableSetWrapper or something like that.
On Mon, May 30, 2022 at 11:50 AM John Hendrikx
<[email protected]> wrote:
Sorry, I misunderstood, I missed that the methods weren't
already
defined in ObservableMap, so no existing signature is changed.
--John
On 30/05/2022 09:39, Tom Schindl wrote:
> Hi,
>
> Well the binary compat IMHO is not a problem. If your subtype
> overwrites the return type of a method the compiler will
inserts a
> bridge method:
>
> Take this example
>
> package bla;
>
> import java.util.ArrayList;
> import java.util.Collection;
> import java.util.List;
>
> public class Test {
> public interface IB {
> public Collection<String> get();
> }
>
> public interface I extends IB {
> public List<String> get();
> }
>
> public class C implements I {
> public ArrayList<String> get() {
> return new ArrayList<String>();
> }
> }
> }
>
> if you look at C with javap you'll notice
>
> Compiled from "Test.java"
> public class bla.Test$C implements bla.Test$I {
> final bla.Test this$0;
> public bla.Test$C(bla.Test);
> public java.util.ArrayList<java.lang.String> get();
> public java.util.Collection get();
> public java.util.List get();
> }
>
>
> The problem is more that if someone directly implemented
ObservableMap
> him/her self that it won't compile anymore. So it is a source
> incompatible change.
>
> Tom
>
> Am 30.05.22 um 08:58 schrieb John Hendrikx:
>> It's not binary compatible, as changing the return type
results in a
>> new method that compiled code won't be able to find.
>>
>> See also "change result type (including void)" here:
>>
https://wiki.eclipse.org/Evolving_Java-based_APIs_2#Evolving_API_interfaces_-_API_methods
<https://urldefense.com/v3/__https://wiki.eclipse.org/Evolving_Java-based_APIs_2*Evolving_API_interfaces_-_API_methods__;Iw!!ACWV5N9M2RV99hQ!Jly4lMnm2UZQsTVKLfmhN7g0AHwp2nlUj4H4a-IfCIp4tqJXElDbEbDsVRhkL6Sa7l097FoQn8_Pi9YS$>
>>
>>
>> --John
>>
>> On 30/05/2022 03:22, Nir Lisker wrote:
>>> Hi,
>>>
>>> Picking up an old issue, JDK-8091393 [1], I went ahead
and looked at
>>> the
>>> work needed to implement it.
>>>
>>> keySet() and entrySet() can both be made to return
ObservableSet rather
>>> easily. values() will probably require an
ObservableCollection<E> type.
>>>
>>> Before discussing these details, my question is: is it
backwards
>>> compatible
>>> to require that these methods now return a more refined
type? I
>>> think that
>>> it will break implementations of ObservableMap out in the
wild if it
>>> overrides these methods in Map. What is the assessment here?
>>>
>>> https://bugs.openjdk.java.net/browse/JDK-8091393
