Re: Mixing self conscious parametrized types with inheritance

From:

Lew <noone@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 13 Mar 2011 16:30:12 -0400

Message-ID:

<ilj9g0$4dp$1@news.albasani.net>

On 03/13/2011 03:36 PM, Robert Klemme wrote:

On 03/13/2011 04:13 PM, Lew wrote:

Robert Klemme wrote:

inspired by our recent discussions of generics I set out to get a clear
picture of how to properly use Comparable<T> - especially when
inheritance
comes into play.

1. Only classes whose methods that use the type parameter may not be
overridden with type specific functionality (either because all
methods or the
class is final, or the type need not change when sub classes override
those)
can do away with the type parameter.

Would you please describe this a bit more fully, perhaps with an
example? I'm not quite getting it.

What's missing from the code at Github? Do you think I should provide another

The explanation of what you meant and how the example demonstrates it.

example? FinalC does not need a type parameter because it cannot get more
specific than this class which is final. Of course we could think of other

I think the business about methods being final is a red herring. You don't
have to express a type parameter when you've completely resolved it. That
isn't about the finality of the subtype or its methods but about the
completeness of type-parameter resolution.

examples as well, e.g. a class hierarchy where parts decide to fix the type
parameter:

class Base<C extends CharSequence> {
public void process(List<C> lc) ...
}

class Derived1<C extends CharSequence> extends Base<C> {
@Override
public void process(List<C> lc) ...
}

class Derived2 extends Base<String> {
@Override
public final void process(List<String> ls) ...
}

Derived2 does not need a type parameter because someone decided to settle with
String for the type and disallow overriding of this method in sub classes.

Again, this is not about whether the method is final.

Thanks for your answers. I need to take some time to digest them and to do my
own experiments. I think I see what you're trying to accomplish now.

--
Lew
Honi soit qui mal y pense.