Re: nested generic HashMap problem

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 27 Apr 2010 12:02:49 -0700 (PDT)

Message-ID:

<037c0387-c29d-4766-9cff-ed6166b71554@k41g2000yqf.googlegroups.com>

Chris Riesbeck wrote:

I don't follow the "don't have a type" part here. The correlation I was
trying to capture was

T get(Demo<T>, long)

using an underlying Map(Demo<T>, Map<long, T>). That seems to me to be
well-defined, just not definable in Java.

Lew wrote:

What do you mean, not definable? That's exactly how you define it,
what you wrote just there, modulo the typos.

class Registry <T>
{
private final Map <Demo <T>, Map <Long, T>> demoMaps =
new HashMap <Demo <T>, Map <Long, T>> ();

...
}

--
Lew

Don't quote sigs.

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>.

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

--
Lew
don't quote sigs