Comment by pjmlp

Lots of implementations and industry standards, many mix Java with OpenJDK.

It is not, Java is like C, C++, JavaScript and co.

There are many implementations, the language and runtime are evolving by industry partners, you get bare metal implementations with real time GC like PTC and Aicas (doing AOT for decades), JIT caches, cloud based JIT compilers (OpenJ9 and Azul), pauseless GC, an LLVM like compiler development framework (Graal),....

There are industry standards like Microprofile and Jakarta EE, which several vendors base their frameworks and application servers on.

And a mobile phone platform, which while isn't proper Java compliant, has enough pieces into it that makes it easier to integrate Java code and libraries, than using Xamarin.

Microsoft actually bothered with ECMA during the early days, however it hasn't been updated since C# 7.3, .NET Framework 4.8.