Proposal: Bump minimum JDK for JavaFX 25 to JDK 23 (more generally, set min for JavaFX N to JDK N-2)

[Kevin Rushforth]

All,

Even though we build JavaFX 25 binaries with JDK 23 (which is being 
updated to JDK 24 this week), as the boot JDK, the latest version of 
JavaFX still runs with JDK 22, although it isn't tested with older JDK 
versions.

In order for JavaFX to be able to use more recent JDK features, we 
should increase the minimum version of the JDK that can run the latest 
JavaFX. Additionally, there is an ongoing cost to keeping JavaFX 
buildable and runnable on older versions of Java, and little reason to 
continue to do so.

I propose to bump the minimum version of the JDK needed to run JavaFX 25 
to JDK 23. I further propose to adopt a standard practice of setting the 
minimum JDK for JavaFX N to JDK N-2. JavaFX N is primarily intended for 
use with JDK N; we also build and test it against JDK N-1 (which is 
typically what we use as the boot JDK). Anything older than that, 
including the proposed minimum JDK N-2 (23 in this specific case), is 
untested.

I filed JDK-8359387 [1] to track this and prepared PR #1827 [2]. This 
will *not* affect update releases of earlier versions of JavaFX (e.g., 
JavaFX 24.0.NN or JavaFX 21.0.NN), which will continue to run with the 
same minimum JDK that they run on today.

Note: in keeping with the "tip and tail" model [3], developers who want 
to run their application on an LTS of the JDK should also get a 
corresponding LTS of JavaFX.

Comments are welcome.

-- Kevin

[1] https://bugs.openjdk.org/browse/JDK-8359387
[2] https://github.com/openjdk/jfx/pull/1827
[3] https://openjdk.org/jeps/14