I have been working in the enterprise Java field, mostly for financial institutions, for about seven years. Beyond core Java, what are "parts" of Java I should know by now? Should as in it will be useful either to nail the interview, or in an actual job. For example, I have never used JSP beyond "hello, world", but I don't suppose that it's something I need to go learn. But I have got core Spring pretty well done. I've read up on GC but that was a while back and need to re-visit it. I'm looking for one suggestion per post please.