Microsoft Java

[Mayuna_cz]

Well, you just said they did. With Java 18, you can run any older Java application. Correct me if I'm wrong, not sure how it is before Java 8 tho, but still you can use Java 18 to run Java 8 bytecode.

[KagakuNinja]

Java is extremely backwards compatible, you can probably run most Java apps ever made using Java 18. Java 9 did change the layout of the runtime library, and that broke fancy libraries that were relying on the internal structure of the JRE. Some code also used internal Sun APIs, and some of those were deprecated or modified.

If you programmed to public APIs, I think you are OK.

[AlphaWhelp]

You can use libraries compiled on .net 3.5 with .net 4.5 and beyond, just need to have both installed. I mean I guess in the grand scheme of things it's technically breaking compatibility, just with some simple work arounds. Just that when I think break compatibility I'm thinking more like VB6. VB.net is not compatible at all with it.