OK but again what's the use case for that? Can you not just use a new version of Java for all your projects, at most setting -source/-target in your project configuration? Certainly in the old days it was always backwards compatible, at least enough that you could develop under a current version and maybe just have a CI job to check that your code still worked on old versions.
In a large organization with hundreds of business-critical Java applications you can bring them all up to one version at once.
It’s quite normal to have multiple versions of JDK being used by different applications
