Cross-compilation support for Java & OpenJDK 8

[tribbloid]

Currently, running ./gradlew test under Java 8 generates the following output:

$ ./gradlew test

...

FAILURE: Build failed with an exception.

* What went wrong:
java.lang.UnsupportedClassVersionError: org/openjfx/gradle/JavaFXPlugin has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0
> org/openjfx/gradle/JavaFXPlugin has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 362ms

This seems to imply that support for Java 8 and OpenJDK 8 (which is still the mainstream java environment due to license issues) is discarded in favour of java 11.

Can we revise the gradle build file such that it supports cross-compiilation for both Java 8 and Java 11?

[breandan]

Good point, thanks for the heads up. JavaFX is not strictly required unless you want to render the plots, so we might as well remove this dependency altogether.

[tribbloid]

Thanks a lot, Does OpenJFX has a variant compatible with JVM 8? I may submit a refactoring to leverage this

[breandan]

I don't remember the exact story but IIRC originally it was packaged with JRE 8 then it was spun off into a separate project around 11. Probably best to just remove the dependency and create a separate Gradle project for the demos. Everything else is JRE 8 compatible.