Re: nested generic HashMap problem

Lew <>
Tue, 27 Apr 2010 19:16:32 -0400
Chris Riesbeck wrote:

That defines a Map of Maps of one type T. I.e., you can make one
Registry where an instance of Demo<Book> retrieves a Map of type<Long,
Book>, and another Registry where a key of type Demo<Author>
retrieves a
Map of type<Long, Author>.

But you can't define a single Registry where a Demo<Book> retrieves a
Map<Long, Book> and Demo<Author> retrieves a Map<Long, Author>.

Lew wrote:

That isn't what you asked for in the post to which I replied.

Daniel Pitts wrote:

It has been the problem that the OP has been trying to solve this entire

In which he referred to wildcarded generics. In the post to which I
responded, he seemed to have changed tack and remarked on what on the surface
was a very specific point. While true, Daniel, your point is irrelevant.

I believe that what the OP is doing is best served by finding some upper-bound
type for the keys, at least, of the primary and secondary map layers, and
using it for T, perhaps making the secondary value simply 'Object'. What
they're trying to do is never going to be painless.

Their desire to have the structures be typeless dooms them to conflict with
the heart of generics. They will have to cast somewhere. Fortunately, they
have a class token buried in all that goop, so they can at least hide the
'catch (ClassCastException ex)' blocks down in the depths and throw only
runtime exceptions. They'll need to Javadoc the hell out of the structures so
that everyone knows that everything has to match the class token.

As I finished typing this I see your other post, Daniel, where you made many
of these points as well.


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