Maybe they want to avoid java coding patterns. FactoryFactoryGenerator kind of stuff. Maybe they want to teach their own java coding patterns and want someone coming in with a blank slate so they don't have to unlearn habits. Maybe they're tired of diploma mill programmers applying and are using this as a resume filter tripwire.
reading this just gives me the biggest imposted syndrom and reminds me of how underqualified for any job i feel, even after my software development apprenticeship
Once I asked a professor to participate in a project. So he interviewed me and asked me about my skills, as they do, and one of the questions was "do you know oop? Java?", me: "just the basics", him: "even better".