ListProperty::bind has different behavior than StringProperty::bind when observables are equal

[Jeanette Winzenburg]

sounds a bit like https://bugs.openjdk.java.net/browse/JDK-8094799 -  
listProperty was fixed for notification of changeListeners to test  
against identity always, should do in binding as well, IMO

Zitat von José Pereda <jose.pereda at gluonhq.com>:

> Hi,
>
> We have come across a possible issue that affects bind() over different
> types of properties.
> We are not sure if it's a bug or it behaves as it should be. Therefore, we
> are reaching out to the community for insight.
>
> See these short code snippets below:
>
> Snippet 1. StringProperty (could be other like IntegerProperty)
>
> StringProperty a = new SimpleStringProperty();
> StringProperty b = new SimpleStringProperty();
> StringProperty c = new SimpleStringProperty();
> c.addListener((obs, ov, nv) -> System.out.println("Change: " + nv));
> c.bind(a);
> c.bind(b);
> b.set("One");
> System.out.println("c contains: " + c.get());
> ====
>
> Snippet 2. ListProperty
>
> ListProperty<String> a = new
> SimpleListProperty<>(FXCollections.<String>observableArrayList());
> ListProperty<String> b = new
> SimpleListProperty<>(FXCollections.<String>observableArrayList());
> ListProperty<String> c = new SimpleListProperty<>();
> c.addListener((ListChangeListener.Change<? extends String> change) ->
> System.out.println("Change: " + change));
> c.bind(a);
> c.bind(b);
> b.add("One");
> b.add("Two");
> System.out.println("c contains: " + Arrays.toString(c.toArray()));
> ====
>
> While snippet 1 produces:
>
> Change: One
> c contains: One
>
> as expected, snippet 2 produces:
>
> Change: { [] added at 0 }
> c contains: []
>
> But the expected result is:
>
> Change: { [] added at 0 }
> Change: { [] added at 0 }
> Change: { [One] added at 0 }
> Change: { [Two] added at 1 }
> c contains: [One, Two]
>
> This expected result only happens by manually doing:
>
> c.bind(a);
> c.unbind(); // need to explicitly unbind
> c.bind(b);
>
> Summing up: when binding a new observable to a bound property, unbind is
> required if that property is a ListProperty, but not a StringProperty (or
> IntegerProperty).
>
> Explanation
>
> In the ListProperty.bind implementation [1] there is a check, and only when
> both current bound observable and new observable are equal, unbind() is
> applied.
>
> The equals is implemented in ReadOnlyListProperty::equals [2] and, being a
> list, follows the List::equals[3] contract, therefore, it compares by items
> of the list.
>
> This is not the case when using other properties like StringPropertyBase or
> IntegerPropertyBase, where bind() is implemented in the same way [4], but
> equals now uses Object::equals[5], so the comparison is now done with ==,
> instead of comparing by the content of each property.
>
> Is this a bug? Should StringProperty, IntegerProperty override equals to
> compare by content and not by object, like ListProperty does? Should
> ListProperty use == operator instead of equals?
>
> This difference in behavior should be at least documented, shouldn't it?
>
>
> Thanks for any input on this,
> Jose
>
>
> [1]
> https://github.com/openjdk/jfx/blob/22d4343fe8563c2931910b98e8f18c6fd4a48f05/modules/javafx.base/src/main/java/javafx/beans/property/ListPropertyBase.java#L268
> [2]
> https://github.com/openjdk/jfx/blob/22d4343fe8563c2931910b98e8f18c6fd4a48f05/modules/javafx.base/src/main/java/javafx/beans/property/ReadOnlyListProperty.java#L110
> [3]
> https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/util/List.java#L542
> [4]
> https://github.com/openjdk/jfx/blob/22d4343fe8563c2931910b98e8f18c6fd4a48f05/modules/javafx.base/src/main/java/javafx/beans/property/StringPropertyBase.java#L161
> [5]
> https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/lang/Object.java#L150
>
> --