Python is the most widely used language, the most popular AI and machine learning frameworks are based on Python (and C/C++ under the hood).
Moreover the vast majority of tutorials, online courses and even academia courses are pushing Python.
Java has only one relatively mature machine learning framework (deeplearning4j). It's said to provide better integration with widely used Java based big data solutions and better portability and product deployment.
The term "Artificial Intelligence" was coined by John McCarthy, the same computer scientist who invented a programming language called LISP. While both theoretical and technological approaches and methods were completely different in those years, LISP is still used for some AI projects. (See Cortex made by ThinkTopic. To be exact, it's based on Clojure, a dialect of Lisp and it runs on JVM.)