Even though we can pass most java interviews (in the east coast:)), I find myself learning bits of practical java how-to on a *daily* basis.
* ant and JVM launch script
* thread pool
* concurrency constructs
* callback listeners
They present everyday challenges to a intermediate developer like me, so better knowledge does improve problem solving, code t r a c i n g and design. These challenges illustrate one reason why I feel less proficient in java than in Perl. I can solve most *practical* Perl problems. Java is bigger and present more “problems”. As I spend more years in java, I hope to pick up more know-how. Therefore java remains my primary study subject, along with c++.
In the list above, I have deliberately omitted vendor products as they aren’t core java IMO. But obviously there’s a lot to learn in them.