Hi Andi,
thanks for your answer. I should possibly have a look at Guava.
As mentioned the problem is not really the DBReader, but the fact, that in
order to fill the list, new instances of T have to created.
So basically the problem can be reduced to:
public class BeanResult<T extends Object> extends ArrayList<T>
{
public BeanResult(Class<T> c, DBCommand cmd)
{
T obj = c.newInstance();
}
...
And the question remains, whether or not it is possible at all, to get rid of
the "Class<T> c" parameter.
I don't really understand, why it is not possible to extract the Class from T.
Regards,
Rainer
Andreas Fink wrote:
> from: Andreas Fink [mailto:[email protected]]
> to: [email protected]
> re: Re: Stupid generics question (possibly)
>
> Hi Rainer.
>
> As long as you do not refactor "new DBReader()" to "new DBReader<T>()"
> there won't be a way around it.
> If you do not need to know the type in "reader.getBeanList" except for
> casting, this Could suffice:
>
> class DBReader<T> {
>
> getBeanList(beanResult, maxItems) {
> ...
> T someData = (T) someMethodCall();
> ...
> }
>
> }
>
> If you need to do more, stick to what you posted (this is how Google
> Guava does it, btw.) or do something funny at runtime using reflection.
>
> The best source for help in cases like this is Angelika Langers generics
> FAQ: http://www.angelikalanger.com/GenericsFAQ/JavaGenericsFAQ.html
>
> Cheers,
> Andi.
>
> On Jul 24, 2011, at 2:00 PM, Rainer Döbele wrote:
>
> > Hi,
> >
> >
> >
> > This might be a stupid question possibly but I just don't feel like
> investigating myself.
> >
> >
> >
> > I have introduced a new simple helper class called BeanResult to
> simplify queries for a list of POJO's a bit.
> >
> > I looks roughly like this:
> >
> >
> >
> > public class BeanResult<T extends Object> extends ArrayList<T>
> >
> > {
> >
> > private DBCommand cmd;
> >
> > private Class<T> type;
> >
> >
> >
> > public BeanResult(Class<T> type, DBCommand cmd)
> >
> > {
> >
> > this.type = type;
> >
> > this.cmd = cmd;
> >
> > }
> >
> >
> >
> > public int fetch(Connection conn, int maxItems)
> >
> > {
> >
> > clear();
> >
> > DBReader reader = new DBReader();
> >
> > try {
> >
> > // Open and Read
> >
> > reader.open(cmd, conn);
> >
> > reader.getBeanList(this, type, maxItems);
> >
> > return size();
> >
> >
> >
> > } finally {
> >
> > reader.close();
> >
> > }
> >
> > }
> >
> > }
> >
> >
> >
> > In order to use it, I must write the following:
> >
> >
> >
> > BeanResult<SampleBean> result = new
> BeanResult<SampleBean>(SampleBean.class, cmd);
> >
> >
> >
> > What I don't like is, that I have to pass the SampleBean.class in the
> constructor.
> >
> > I would rather just write:
> >
> >
> >
> > BeanResult<SampleBean> result = new BeanResult<SampleBean>(cmd);
> >
> >
> >
> > This is beause the getBeanList uses type.newInstance() to create new
> Instances of the bean.
> >
> >
> >
> > Does anyone know whether and how to determine the Class from T or
> another option to get rid of this extra parameter.
> >
> > I have checked the code in under the EMPIREDB-99 branch.
> >
> >
> >
> > Regards
> >
> > Rainer
> >
> >
> >
>
>
> --
> web: http://andreasfink.com/
> mail: [email protected]
> mobil: +34 65 1728443
> tel: +34 93 2082949
