Re: Can this callback mechanism be generified?

From:

Casper Bang <casper@jbr.dk>

Newsgroups:

comp.lang.java.help

Date:

Mon, 05 May 2008 04:01:44 +0200

Message-ID:

<mUtTj.3143$J46.25175@wagner.videotron.net>

Mark Space wrote:

I agree this part is easier to read, I just don't see the rest of the
code much improved (pulling the type by name from the interface name was
a pretty good trick. With luck, we'll get reifiable types in Java 7 and
then nonsense like that will be unneeded.)

I did some reading (Java Generics and Collections) and it turns out
there are ways to get to the types, in spite of erasure. So now I do it
a bit cleaner, no pulling apart a string and no reflection required:

private <T> Class extractGenericType(Callback<T> callback)
{
     Type[] interfaces = callback.getClass().getGenericInterfaces();

     if(interfaces.length != 1 || !(interfaces[0] instanceof
ParameterizedType))
         throw new RuntimeException("You must supply a generified
Callback with a single parameterized type");

     Type[] parmTypes =
((ParameterizedType)interfaces[0]).getActualTypeArguments();

     return (Class)parmTypes[0];
}

I might be off base here, I haven't had a need to play around with
generic beyond basic functions, so please take this as discussion, not
dogma.

Of course. :) Thanks a lot for the feedback!