Like I said, there are six ways to Sunday to do everything the way you
want it.
I just disagree with that/your approach.
Cheers,
-Polar
Glynn, Eoghan wrote:
-----Original Message-----
From: Polar Humenn [mailto:[EMAIL PROTECTED]
Sent: 04 April 2007 14:57
To: [email protected]
Subject: Re: Checkstyle
I would firmly have to disagree.
You have lots of generated code that are classes, don't use
interfaces, which people have to use to use the API. But I digress.
What generated code exactly is in the form of classes (that the user has
to extend)?
At least for JAX-WS, the main bit of generated code exposed to users is
the SEI, where the "I" stands for interface.
Clearly I'm not saying don't use classes. You can't program any
executable logic into interfaces.
What I'm saying is, if the user is to extend or implement some of our
code, give them the option to implement an interface. What's so
controversial or disagreeable about that?
If I am to use a *class* like:
final class UserPass {
final String user;
final String pass;
UserPass(String u, String p) {
user = u; pass = p;
}
String getUser() { return user; }
String getPass() { return pass; }
}
I have a contract with the an operation
UserPass getUserPass();
That what I get back won't change. It wont deliver different
things for subsequent calls to getUser or getPass.
So keep UserPass as a class!
The point is that the application code wouldn't need to extend UserPass
anyway.
What they do need to extend is the HttpBasicAuthCredsSupplier. So that
should be an interface. And also possibly an abstract class implementing
it, if it contains any non-trivial bolier-plate code. So that the user
has the choice to extend or implement.
So assuming HttpBasicAuthCredsSupplier is an interface, then UserPass
could be either an inner interface (if want to keep the inner/outter
scoping), or a stand-alone class (if you want to control the
implementation). Take your choice.
This allows me to make certain assumptions on the calling
side that I cannot make if UserPass was forced to be an
interface. Such as I can cache the object instead of the
results. And I have some assurance that there are no convert
channels from it.
Covert channels?
Sure, you can put a certain Abstract logic built "immutable"
class underneath it, but it doesn't *mean* the same thing. I
can't *guarantee* immutability from the calling side, if all
I'm requiring it be is an interface.
No-one is requiring UserPass to be an interface. As the user would never
have to extend it, it doesn't really matter.
But you can easily get the immutablility you want even if UserPass is an
inner interface (assuming the inner/outter scoping was more important to
you). As Java strings are themselves immutable, just extract the
username & passwd fields from the returned value and re-wrap in a
trivial immutable UserPass impl.
On the other hand, if you want to dictate the actual UserPass impl, then
make it an outter class.
No rocket science. And not worth the time that's already been burned on
this discussion either.
Nope, I don't buy the argument.
The other thing, I can alleviate memory leaks somewhat
because if it were an interface and somebody decided to give
me an implementation of it as an inner class and I cached the
object I end up keeping a reference to the whole outer class.
A *static* inner class (like the UserPass in your patch) has no
reference to the outter class.
Only a *non-static* inner class carries a reference to an instance of
the outter class.
/Eoghan
The basic upshot is that you can implement it any number of 6
different ways to Sunday but the "contracts" *are* different,
subtle as they may be.
Cheers,
-Polar
Glynn, Eoghan wrote:
Well the mumblings were more like advice to use interfaces *in
addition
to* abstract classes, not *instead of* abstract classes.
Plus some pointers to Java features/idiom like @Override, inner
interfaces, composition v. inheritance, that would solve
some of the
problems Polar perceives.
However there *is* a compelling reason for casting public APIs in
terms of interfaces, as opposed to the corresponding
abstract classes.
We generally do not want to *force* users to extend our abstract
classes and use up their one shot at implementation inheritance in
doing so, just to get some boiler-plate code.
Example would be Polar's HttpBasicAuthSupplier. That should be an
interface, possibly also implemented by an abstract class
holding the
boiler-plate logic. A user may want to directly implement the
interface themselves if they needed to extend a different
base class
for some reason, e.g. DialogBoxHttpBasicAuthSupplier
extends GUIWidget
implements HttpBasicAuthSupplier.
So the abstract base class is in my view a convenience that
the user
may choose to take advantage of, or not, as the case may
be. But they
should not be forced to do so. So AbstractWSFeature is
grand, as long
there's also a WSFeature interface that the user can choose to
implement directly.
Sure, users who make that choice would be impacted more by future
additions to the interface. But in reality, not all new
methods would
have a sensible default impl that extensions of the
abstract class can
just pick up without any change.
As far as the Abstract* naming convention is concerned, I'm
not a big
fan of such rules when forced to change my own class names,
but once
you get over that irritation I can see the value of the consistency
that the rule brings. So I'm not pushed either way.
Hey, it could be a lot worse ... at least we don't have the
C# IFooBar
naming scheme for interfaces :)
Cheers,
Eoghan
-----Original Message-----
From: Dan Diephouse [mailto:[EMAIL PROTECTED]
Sent: 04 April 2007 00:50
To: [email protected]
Subject: Re: Checkstyle
I completely agree that we should get rid of this rule.
First of all, Aegis from XFire use Type which is abstract, and I
don't want to change this for migration reasons which is
one of the
reasons pmd is disabled for this module.
Second, I agree that the Abstract/base/factory naming is
incredibly
awkward.
I hear some mumblings of "just use interfaces" - but
abstract classes
provide a much more robust way to add features in the
future. With an
interface, if you add a method, it will break every class that
implemented that interface. With abstract classes if you add a new
method, all you need to do is provide a default
implementation of it
and everything will work swell in the future. So I tend to use
abstract classes more and more to avoid future incompatibilities
(AbstractWSFeature, AbstractServiceFactoryBean,
AbstractEndpointFactory). With at least the first two, I
would like
to get ride of the Abstract.
- Dan
On 4/3/07, Polar Humenn <[EMAIL PROTECTED]> wrote:
Is there a "good" motivation of why "abstract" classes have to be
named "Abstract" "Base" or "Factory"?
If a class is declared "abstract", I want the *compiler* to
tell the
developer that s/he has not filled out a particular
functionality when
s/he extends the abstract class. Not that I want it named
"Abstract".
For example,
abstract class Muffin {
......
abstract Kind kind();
}
I really don't want my code littered with method definitions like:
void eat(AbstractMuffin muff) {
I want it to be:
void eat(Muffin muff);
because that's what it is. It's not an AbstractMuffin, it's
a Muffin!
Can we get rid of that particular checkstyle rule?
I say that, because it forces, either
a) illogical names, like AbstractMuffin, to be used in
definitions,
making for
awkwardness. (i.e. eat(AbstractMuffin muff);
b) default implementations, just to avoid the illogical names!
This particular avoidance causes errors to be caught
at run time
instead of compile time, where it should be caught! And
sometimes causing
a loss of time to find it.
For example, with the current checkstyle rule I could be
forced to
write the class with a default implementation expecting it to be
overridden. (Except there is no way to tell a compiler that).
class Muffin {
.....
Kind kind() {
return Kind.BLUEBERRY;
}
}
void eat(Muffin muff) {
System.out.println("I'm eating a " + muff.kind() +
" muffin!");
}
and a developer goes ahead and writes:
class CornMuffin extends Muffin {
Kind kiend() {
return Kind.CORN;
}
}
and it compiles fine without problems. Subsequently he
can't figure
out why his application still says he has a BLUEBERRY muffin,
especially when he has used "eat(new CornMuffin())".
This kind of pattern complete adverted the use of compiler
protections.
Cheers,
-Polar
--
Dan Diephouse
Envoi Solutions
http://envoisolutions.com | http://netzooid.com/blog
