A problem is taking a company's entire Java codebase that's been running on Oracle JRE's, compiled with Oracle JDK's, written to work around Oracle bugs, for a decade, then trying to throw that on OpenJDK JRE's, compiled with OpenJDK JDK's. If it's a huge codebase then performance and runtime errors alone are concerning enough to stay frozen on 8 for as long as possible, without even considering code migration.

> just go with Fedora

I'm not disagreeing with this at all, but I do want to point out this was CentOS a couple months ago!

I'm sure you know exactly what you're talking about... but I can't really imagine what major incompatibilities you're seeing while doing these upgrades. Java is amazingly backwards-compatible in my experience. I don't think I've ever had to change anything during an upgrade, in my entire career, except sometimes a couple of minor things to do with Unsafe. I'd love to hear more and some concrete examples if you're able to.

I have no experience in upgrading Java versions or the corresponding code changes required. I have witnessed runtime differences, related to performance and GC behavior, from Oracle 8 to OpenJDK 8 that were unexpected enough to warrant temporarily sticking with Oracle in exactly one case.

That is eons ago, in Java 8 there were indeed differences between Oracle JDK and OpenJDK, this in no longer true since Java 10, even less so in Java 16.

Now, Java like C or C++, enjoys multiple implementations, so even across OpenJDK, J9, Azul, PTC, Aicas,..., there will be differences.

And that's why you have tests...

Having migrated some respectably sized projects to OpenJDK in my experience it's more work to migrate a codebase to a new Java major version than from Oracle to OpenJDK.

Are you serious? I've seen several large legacy Java applications move to OpenJDK without a problem.

> OpenJDK and Oracle Java are as different as Red-Hat Fedora and Red-Hat Enterprise Linux.

In a comment in another sub-thread you said "Except that since several releases Oracle Java is basically OpenJDK + Support." But that would be more like CentOS and RHEL, not Fedora and RHEL.

Whatever, the point being that since the last couple of releases OpenJDK and Oracle JDK differences are mostly about support, and license of using JFR in production.