RFR: 8339603: Seal the class hierarchy of Node, Camera, LightBase, Shape, Shape3D

[Andy Goryachev]

On Thu, 5 Sep 2024 12:01:23 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

> None of these classes can be extended by user code, and any attempt to do so will fail at runtime with an exception. For this reason, we can seal the class hierarchy and remove the run-time checks to turn this into a compile-time error instead.
> 
> In some cases, `Node` and `Shape` are extended by JavaFX classes in other modules, preventing those derived classes from being permitted subclasses. A non-exported `AbstractNode` and `AbstractShape` class is provided just for these scenarios. Note that introducing a new superclass is a source- and binary-compatible change (see [JLS ch. 13](https://docs.oracle.com/javase/specs/jls/se22/html/jls-13.html)).
> 
> I'm not sure if this change requires a CSR, as it doesn't change the specification in any meaningful way. There can be no valid JavaFX program that is affected by this change.

modules/javafx.graphics/src/main/java/javafx/scene/Node.java line 421:

> 419: public abstract sealed class Node
> 420:         implements EventTarget, Styleable
> 421:         permits AbstractNode, Camera, LightBase, Parent, SubScene, Canvas, ImageView, Shape, Shape3D {

We may need to use stronger wording in javadoc in regards to extending Nodes.  should -> must, etc.  (or, rather, 'cannot' and possibly explain why?)

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PR Review Comment: https://git.openjdk.org/jfx/pull/1556#discussion_r1747442948