[jdom-interest] instanceof

Syloke Soong ssoong at protedyne.com
Mon Jan 22 08:18:50 PST 2007

Two weeks ago, CNN.com gallery had an article querying the mystery
behind an old fading picture where a man was sitting on a dead horse in
a town square in Minnesota, circa late 1800's. Incidentally, the weeks
prior were a deeded community's uproar in Colorado about how
anti-American and anti-C over a member's use of a peace wreath as xmas
decoration prominently outside her house. 

I am about to sit on a dead horse. Last month, we had a rather cute
debate on the academics of the propriety of using instanceof and how
anti-object-oriented it is. I have heard that some oo-purists feel
instanceof should be banned or obliterated from the java language (or
any language). I think use instanceof in java seems as anti-OO as the
use of peace wreath for xmas is anti-American.

Enough already on that rambling preamble.

The reason I am musing over this is, besides attempts at detracting from
and, the consequence of, my current frustration on looping over

I have not much choice but to test each iterator member with instanceof,
do I?

I mean, if I had a sudden obsessive compulsion to make OO-purists happy,
what should I do with the next() member of the iterator extracted from

Even if jdom had a getContentIterator() from which next() would produce
a Content object rather than a bland Object, and that Content had a
getContentType() which could be either {Element | Text}:

[hypothetical code]
public contentious(Element ej)
  ContentIterator citr = ej.getContentIterator();
    Content citrus = citr.next();

public Consume(Text t){...}
public Consume(Element e){...}

[/hypothetical code]

Now the two Consume methods would be useless should rather be:

[hypothetical code]
    Content citrus = citr.next();
    Consume(citrus.getContentType(), citrus);

public Consume(Class x, Text t){...}
public Consume(Class x, Element e){...} 
[/hypothetical code]

As I said, in the event of my sudden upheaval in life and turned into an
abrupt oo-purist - then I would object to using

Consume(Class classflag, Content cj);

It should be purely Consume(cj);
cj should autonomously tell its own bearing without aid of a flag.

A method should digest an object without further hint. It should
decipher what that object is without a hinting flag. That is the spirit
of the OO I believe in. Imagine, someone handing me a vehicle to paint,
I should look at it and know it is a truck or a car or a plane without
further ado.

Using classflag is cheating. A method should consume an object, decipher
it without the aid of an external flag. It's like the Republican tax
reduction effort. I either pay it at the federal level or it gets
reduced where my state and town finally forced me to pay the shortfall.
Somewhere there is an instanceof.

I surmise the proper way is casting the call:
Consume( (classflag)cj);

Consume( (cj.getContentType)cj),

but the java language (or according to Sun's legal binding, Java
platform), does allow the result of method to be used as a cast.

Rolling moss gathers no stone. Or is it, A rolling stone gathers no
moss. I'm rolling from one level of OO-purification to the next().
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