Re: (Class>) casting troubles

[Sebastiaan van Erk]

Zappaterrini, Larry wrote:

In the example you have detailed, RawBar is not a subtype of Bar<?>
since it extends the raw type Bar.

  Bar<?> bar = new RawBar();



Regards,
Sebastiaan

I guess it depends on the definition of subtype. It is at least the case that the following assignment compiles without warnings (without warnings about unchecked casts): So is it then a subtype? Or isn't it? It's all terribly inconsistent if you ask me. :-(

-----Original Message-----

From: Sebastiaan van Erk [mailto:[EMAIL PROTECTED] Sent: Friday, June 06, 2008 11:31 AM

To: users@wicket.apache.org
Subject: Re: (Class<? extends Page<?>>) casting troubles

ARgh, you always make typos with this stuff.

See correction.

Sebastiaan van Erk wrote:

Martin Funk wrote:

Class<? extends Page<?>> means "class of (anything that extends

(page of

anything))".

I'm not so sure.

There are 2 separate issues:



  static class Foo<T> {
  }

  static class Bar<T> {
  }

  static class RawBar extends Bar {
  }

  static class SubBar<T> extends Bar<T> {
  }

Thus:

   Bar<?> bar = new RawBar(); // works, because RawBar is a subtype of

ISSUE 1: Foo<? extends Bar<?>> is not assignable from a Foo<RawBar> where RawBar extends Bar as a raw type. That is, given:

Bar<?>

But:

   Foo<? extends Bar<?>> rawbar = new RawBar(); // DOES NOT WORK -

THIS

IS CAUSING ONE HALF OF ALL OUR HEADACHES

(correction:)
    Foo<? extends Bar<?>> rawbar = new Foo<RawBar>(); // DOES NOT WORK -

THIS IS CAUSING ONE HALF OF ALL OUR HEADACHES

Btw, this does work (like you expect):
    Foo<? extends Bar<?>> rawbar2 = new Foo<SubBar<?>>();

Note that this is the issue that complete baffles me, as RawBar is a subtype of Bar<?>, so I *really* *really* *REALLY* have no idea why

the

compiler chokes on this.

ISSUE 2: The class literal of a generic type returns a class of a raw type. Thus Foo.class return Class<Foo>. This is also really messed

up,

because:




x fc = Foo.class;

Class<Foo> fc = Foo.class; compiles, but generates a warning (reference to raw type). But if you type this in eclipse: and use eclipse quickfix to change "x" to the "correct" type, it'll change it to precisely Class<Foo> (the JLS is very short about this,

see

also

http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#1

5.8.2).

So what the heck is the proper type for the class literal??? I

couldn't

find any!

Finally, note that when you define a method like this:

  static void method1(Foo<? extends Bar<?>> y) {
  }

it works like a charm for a new Foo<SubBar<String>>, i.e., the "Foo of

(anything that extends (bar of anything))" really is the correct interpretation.

Regards,
Sebastiaan

It's just that the interaction with raw types is completely *foobar* (pun intended).

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