An extesion that makes AdopOpenJDK-12 available for Tiny Core Linux has been published in the main Tiny Core Linux repository.
AdoptOpenJDK is a build of OpenJDK. In other words, now you can run modern Java programs in Tiny Core Linux using this extension. Keep in mind that AdoptOpenJDK is not available for i386 and that this extension is only available for amd64.
I made this extension by repackaging the official binaries provided by the AdoptOpenJDK project. The main issue this apporach has is that the size of the extension is very big. I will look into building a slimmer one in the future.