Dear All,

We all know EJB3 annotations are very, very clever things. Much cleverer than, for example, someone like me.

So here's my puzzle: if Java generics are implemented using erasure, such that type information is unavailable at runtime, how do the EJB3 annotations extract the type information in a case such as...



...in order to know we are talking about a List of Kittens, not just Objects?

The doco suggests EJB3 does indeed do this, but I'm fascinated to know how.

Thanks and great job guys!

When I say the 'doco suggests EJB3 does indeed do this', I am referring to...

[url]
http://www.hibernate.org/hib_docs/annot ... ollections
[/url]

...where it says...

Hehe. Type erasure is not quite that thorough. :-)


You can still get the generic type using reflection.

Gavin,

Thanks for such a quick response. I found a great example of this at...

http://joe.truemesh.com/blog/000495.html

...it is strange, though, I wonder if all the people complaining about erasure know that you can just hop over to the Class and read the generic type information from there? I think that will make a lot of people very happy.

I get the feeling the whole 'erasure' message hasn't been communicated very well.

Well, one of the problems is that most of the time people writing blogs or posting on TheMuppetShow.com saying "this is shit", "this sucks" (which is about the depth of most blogs in the Java community) have not *actually* taken the time to really understand the thing they are using and research the reasons why the design decisions were made by people who most probably spent *way* more time thinking about the problem than they did.

I'll stop ranting ;)