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.
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.
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.
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.
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.
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
