[ajug-members] design

[Wilson, Jeff]

You stop when the model is sufficient for your problem domain.

Reuse is most often a red-herring -- you probably will not reuse a Person class developed for a College registration system in a Patient care system. The domains are different; so will the behavior and the data.

Don't think of it as modeling. You're not trying to model the real world, that has higgs-boson particles or quantum foam. You're trying to model a (for example) Student registering for classes. The software model for Student registration doesn't care if the Student has three heads, is cold-blooded, or has malarial. It only cares if the Student has an Address, a Student Number, and $3500 per quarter.

+jeff (MJW)
---

"The first 90% of the code accounts for the first 90% of the development time. The remaining 10% of the code accounts for the other 90% of the development time."
      -- Ninety-Ninety Rule

---------------------------------------------
M. Jeff Wilson, Lead Member Technical Staff
AT&T Services, Inc.
Operations & Service Dev
jw9615 at att.com 
+1 404.499.7235

-----Original Message-----
From: 521 [mailto:521 at ofig.org] 
Sent: Thursday, February 19, 2009 11:20 AM
To: ajug-members at ajug.org
Subject: Re: [ajug-members] design

cool, tks jeff
>>The methods are considered to be the behavior of the object.
-i get freaked out, hehe, and then get no-where-
when i write stuff down on paper before i type-out classes in a simple 'math' 
game or a simple 'dog-walking' game; i get very-darn caught up in how deep do 
i go?  i find my mind arguing with itself on how far do i break down an 
object into the parts (for future use, code-reuse) it is made up of; say a 
person's hand, wrist/hand/finger/hair/finger-nail/bone/joint/vein/blood/blood-
flow/blood-cell/cell-division/hand-shake/snap-fingers/thumb's-up/thumb's-
down/shoot-bird/fingernail-growth/broken-finger/heal/cell-division/skin-
cancer/make-a-fist/finger-smashed-in-door/wooooh-nilly/ doe!  -a class is 
blueprint of blueprints down to the higgs-boson, the derivation of 
mass/matter itself

barclay


On Thu, 19 Feb 2009 10:32:04 -0500, Wilson, Jeff wrote 
> In general, the accepted way most people look at objects are that they 
> are the "nouns". Methods that work on the objects are the "verbs". 
> Systems are built by having a network of objects that invoke methods on 
> each other. 
> 
> Some nouns will be concepts in your business domain or problem space. 
> Other nouns are computer science concepts like sessions, transactions, 
> threads, etc. 
> 
> That is an incredibly simplified view of the world of OO. It misses a 
> lot of good design practices, conventions, and so many other concepts 
> that I can't list here, but I will list some other crucial points: 
> 
> Objects represent a concept and have methods that conceptually map onto 
> those concepts. 
> 
> Objects contain data that are needed to support that concept. 
> 
> The methods are considered to be the behavior of the object. 
> 
> The data in an object should not be exposed to the rest of the 
> application unless that exposure is a part of the concept. (Arguably, 
> most classes should not contain getter or setter methods for their 
> fields, and all fields should be private.) 
> 
> I assume you are comfortable with procedural code, in which you've got a 
> bunch of functions and pass around data structures between them. Robert 
> Martin, in his book _Clean Code_, makes this statement about the 
> differences between procedural and OO code: 
> 
> "Procedural code makes it easy to add new functions without changing the 
> existing data structures. OO code, on the other hand, makes it possible 
> to add new classes without changing any existing function. 
> 
> "Procedural code makes it hard to add new data structures because all 
> the functions must change. OO code makes it hard to add new functions 
> because all the classes must change." 
> 
> +jeff (MJW) 
> --- 
> 
> "The first 90% of the code accounts for the first 90% of the development 
> time. The remaining 10% of the code accounts for the other 90% of the 
> development time." 
>      -- Ninety-Ninety Rule 
> 
> --------------------------------------------- 
> M. Jeff Wilson, Lead Member Technical Staff 
> AT&T Services, Inc. 
> Operations & Service Dev 
> jw9615 at att.com 
> +1 404.499.7235 
> 
> -----Original Message----- 
> From: 521 [mailto:521 at ofig.org] 
> Sent: Monday, February 16, 2009 10:04 AM 
> To: ajug-members at ajug.org 
> Subject: [ajug-members] design 
> 
> by design, in java- or oop in general- is it best to have classes made 
> as follows... 
> 
>  -certain classes are designed to be the motors or engines of an 
> application 
>  -certain classes are designed to the the nouns/subjects of the 
> application 
>  -other classes, maybe, some other stuff, etc? 
> 
> barclay 
> 
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