To spin up a temporary environment with a different Java version without touching your real environment, try this Docker command:
docker run -i -t --mount "type=bind,src=$PWD,dst=/code" openjdk:11-jdk bash
(Change “11-jdk” to the version you want as listed on the README.)
Then you can build the code inside the current directory something like this:
cd code ./gradlew test
Or similar for other build tools, although you may need to install them first.