Java is common in exercises IMHO because it is easy to outline patterns and was used for building design pattern understanding. The general readability is high if a dev have some solid experience, very handy. Also, Java’s OOP is “old” enough to have blazed the trail for key ideas. For better or worse, in design, sustainability, and the collective conscious of programming Java has value unlike many other languages.
I personally dislike Java but I do understand the importance as a teaching language as well as a bolt-on solution for larger system needs.
Great article, so much more to discuss.