thanks...
Damon Goodyear
> Date: Fri, 26 Sep 2008 09:53:53 +0100> From: kennym_at_kizoom.com> To: users_at_jaxb.dev.java.net> Subject: Re: JAXB Generic> > No problemo.> > I can highly recommend The O'Reilly book on Java Generics. It's > extremely readable, and manages to explain neatly why many things in > generics are the way they are, e.g. why you can't create a generic > subclass of Exception.> > > > Damon Goodyear wrote:> > Do you know that feeling when you sort of know the kind of answer to > > your question but don't know it detail? This is it. I would have > > pratted around for ages in the region of your answer and maybe got it, > > maybe not.> > > > As you say, annoying. Passing two lots of information when one should > > do....> > > > Thanks for the answer...> > > > > > Damon Goodyear> > > > > > ------------------------------------------------------------------------> > > Date: Thu, 25 Sep 2008 22:27:30 +0100> > > From: kennym_at_kizoom.com> > > To: users_at_jaxb.dev.java.net> > > Subject: Re: JAXB Generic> > >> > > > JAXBContext ctx => > > > JAXBContext.newInstance(T.class.getPackage().getName());> > >> > > > ...except that the T.class line is jumped on by the compiler as > > being an> > > > illegal class literal for type parameter T. Also, the compiler moans> > > > about the casting of the object returned.> > >> > > This is the big gotcha of java generics. At runtime, the information> > > about T is lost, so you can't use T.class.> > >> > > You need to pass in another parameter to your method, which is the Class> > > object representing T:> > >> > > public T load(String fileName, Class<? extends T> c){> > > try{> > > JAXBContext ctx = JAXBContext.newInstance(c.getPackage().getName());> > > Unmarshaller u = ctx.createUnmarshaller();> > > JAXBElement rootElement = (JAXBElement) u.unmarshal(new> > > FileInputStream(fileName));> > >> > > w = (T)rootElement.getValue();> > >> > > } catch (...)> > > }> > > return a;> > > }> > >> > > It's annoying, but unavoidable, but the caller of the method knows what> > > T is, so it can pass in the correct class.> > >> > > As for the warning, you just have to live with it, or use > > @SuppressWarning> > >> > >> > > kenny> > >> > >> > > ---------------------------------------------------------------------> > > To unsubscribe, e-mail: users-unsubscribe_at_jaxb.dev.java.net> > > For additional commands, e-mail: users-help_at_jaxb.dev.java.net> > >> > ---------------------------------------------------------------------> To unsubscribe, e-mail: users-unsubscribe_at_jaxb.dev.java.net> For additional commands, e-mail: users-help_at_jaxb.dev.java.net>