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.

What is the benefit of this change?

Also, this change is breaking.  One can currently create a Node:

public class CanCreateNode extends Application {
    @Override
    public void init() {
        Node n1 = new Node() {
        };
        class Yo extends Node {
        }
        Yo n2 = new Yo();
    }

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PR Comment: https://git.openjdk.org/jfx/pull/1556#issuecomment-2332269300