I'm not too bad using primitive variables, but I'm having a fairly rough time trying to productively use the API. An example it recently used TreeMap and it took me a while to discover that it made shallow copies. Examples had used string literals to put stuff into TreeMap, so when I used a variable, it was not obvious at first. In this case I put the stuff into two Vectors first (K & V) and then entered it into TreeMap, and this worked fine. Anyway, I'm bumping into stuff like type mismatches and syntactic subtlties all the time. It makes it hard to plan my code and finding work-arounds is nerve racking. Having to amke little programs to see if a work-around works gets discouraging.
Books packed with running code examples are really helpful. My favorite author is Herb Schildt.
Nevertheless, I feel somewhat at wit's end. Any suggestions helpful.