Whenever code is removed from the Java standard library it is announced ages ahead of time and then typically it becomes available in a separate artefact so you can still use it if you depended on it.
I wrote an online securities trading system in Java, with a little Jython. Java is reasonably good at stability, but I find it unappealing for other reasons, especially for prototyping. Kotlin might be okay.
Jython no longer works with basically any current Python libraries because it never made the leap to Python 3, and the Python community stigmatizes maintaining Python 2 compatibility in your libraries. This basically killed Jython, and from my point of view, Jython was one of the best things about Java.
