API review: fix for TableViewBuilder- reference to create is ambiguous (RT-24272)

[Richard Bair]

Hi Eva,

Yes, we're between a rock and a hard place on this one!

One question: you mention that this is a source incompatible change. But is it a runtime incompatible change? That is, if I have a JavaFX app already compiled against Java 6, and I run it on Java 7 or Java 8, will it break? Or is it only something I have to do to my sources at compile time?

Thanks
Richard

On Aug 24, 2012, at 6:50 AM, Eva Krejcirova wrote:

> Hi All,
> 
> We are having problems with the way our builders are created -
> 
> Basically, this code:
> ChoiceBoxBuilder.<String>create()
>        .id("choiceBox")
>        .items(FXCollections.observableArrayList("item1", "item2"))
>        .build();
> 
> or this one:
> 
> TableView<Job> tableView1 = TableViewBuilder.<Job>create();
> 
> doesn't compile anymore in JavaFX 8.0 when using Java 7 - it fails with error: reference to create is ambiguous, both method create() in RegionBuilder and method <T>create() in ComboBoxBuilder match
>        ComboBox<String> combo = ComboBoxBuilder.<String>create().build();
>  where T is a type-variable:
>    T extends Object declared in method <T>create()
> 
> Unfortunately there is no simple solution for this and the one I am proposing requires some incompatible API changes which are the reason for this email.
> 
> First some background:
> We didn't have this problem up until now because all ancestors of ChoiceBox and other controls were abstract, so there was just one create() method in their builders.
> (this one: public static <T> javafx.scene.control.ChoiceBoxBuilder<T, ?> create() )
> Now however, Control extends Region which is not an abstract class, which means that TableViewBuilder now extends RegionBuilder and inherits create() method from RegionBuilder (this one: public static javafx.scene.layout.RegionBuilder<?> create()). And the compiler doesn't know which one of the create() methods to pick (Java 6 compiles this just fine, this issue manifest itself when compiled with Java 7).  Since the behavior of Java 7 is correct, this must be fixed on our side.
> 
> My proposal is to add another create method to parametrized classes which would take the type as an argument e.g.
> 
>    public static <T> javafx.scene.control.ChoiceBoxBuilder<T, ?> create(final Class<T> type) {
>        return new javafx.scene.control.ChoiceBoxBuilder();
>    }
> 
> and make the create() without arguments non-generic, so it hides the create in Region:
> 
>    public static javafx.scene.control.ChoiceBoxBuilder<?, ?> create() {
>        return new javafx.scene.control.ChoiceBoxBuilder();
>    }
> 
> This way, the user can create the builder like this:
> ChoiceBoxBuilder.create(String.class)
>        .id("choiceBox")
>        .items(FXCollections.observableArrayList("item1", "item2"))
>        .build();
> 
> Unfortunately this change will break some already existing code (but I don't see any better way for solving this).
> E.g. this code:
> ChoiceBox chb = ChoiceBoxBuilder.<String>create().items(FXCollections.observableArrayList("one", "two")).build();
> will still not be compilable and will have to be rewritten (but at least there will be a way to do it).
> 
> I already have the fix ready and I tested that it works but am open to other suggestions how to solve this problem if anybody has some better ones :-)
> 
> Thanks,
> Eva