RFR: 8375588: Enhanced property metadata

[John Hendrikx]

On Tue, 20 Jan 2026 19:25:42 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

> > JavaFX already has this concept today, but we're not using the `Property` API to model it. Layout constraints like `GridPane.columnIndex` or `HBox.margin` are implemented as static getter/setter pairs. Since they are not first-class properties, you don't get any of the nice property features (bindings, listeners, styling, etc).
> 
> I always found this design to be weird and unnecessary - these should be the properties/constraints of the container or the layout, not something stored in the child nodes. What happens when the said child is moved from one container to another??
> 
> It might be just me, but I fail to see the value of this proposal.

This is basically the JavaFX way to attach layout information to nodes, used by `GridPane`, `HBox`, `StackPane`, etc.  In Swing this is handled differently by making layout constraints a 2nd parameter when adding a node (like `GridBagConstraints`), in FX this is done via the general `Properties` map which is much more flexible.  Extending this system so they become full, observable properties, and even styleable properties is a very logical step.  Making them styleable for example will allow you to move them to CSS:


.button {
    -fx-hbox-margin: 10 10 10 10;
    -fx-hbox-hgrow: ALWAYS;
}

This is currently one of the biggest missing features when it comes to styling controls, having to go to programmatic configuration for these kinds of styling properties.

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PR Comment: https://git.openjdk.org/jfx/pull/2015#issuecomment-3775047169