Building the engine with Java 11 is currently possible but it's still built with Java 8 because of a bug in Maven Javadoc plugin:
The very first objective consists in ensuring that the engine builds with Java >= 11 without warnings.
The second objective consists in switching to Java 11 as minimal supported version of Java and in using it to build the binaries from now on.
The third objective consists in creating modules from all projects.
The bug 620 of maven-javadoc-plugin was fixed, I worked around the bug 583 of maven-javadoc-plugin.
I've just successfully built the Java documentation with Java 11 and maven-javadoc-plugin 3.2.0-SNAPSHOT. When the version 3.2.0 is out, I'll be able to build the whole engine with Java 11 and to commit my few changes.
maven-javadoc-plugin 3.2.0 was released in March, I can use it now and it works:
I built the engine without any problem yesterday with Java 14.
The engine can be built with Java 14. Using Java >= 16 requires to use -DforkCount=0 because of EasyMock depending on cglib which doesn't fully support Java >= 16 yet.