CSC223 2004F, Class 34: Design Heuristics, Concluded

Admin:
* Questions on Monday's homework?
* Prospectives!  Whee!
* New reading: Design Patterns, Chapters 1 and 2.

Overview:
* Choosing ways to obtain objects
  * Riel's heuristics
  * Our heuristics
* Debriefing on Riel (if there's time)

notes by Sam(M).  

questions on homework for monday? 
 - yes, we have to integrate everything
 - user interface can suck for now

next:  we're gonna read Design Patterns!
 - for monday, read chapters 1 & 2

quick detour:
  "design patterns are the coolest things since CRC cards" (SamR, 2004)
  CRC cards refresher:
   - put down specifics of class 
   - RPG where everyone gets a character (a class)

Today's promise: Take-homes will be returned *eventually*

Today's topic:  More fun with heuristics!  Riel vs. CSC223:  choosing objects to use

Where do classes get objects to use? 
 - suppose method a.bar() wants to use b.foo(), but doesn't yet have b:
   - a can construct b in bar()
   - a can previously construct b (at initialization, e.g.) --> a contains or assoc. with b
   - a receives b as a parameter
   - a consults a third party for b
     - Riel suggests a fundamental problem with this one:
     	- Where's the third party come from?
   - b is a global variable (e.g., System.out)

Are there heuristics that help us decide which way to get b? 
 - Kat's heuristic: if only one method uses b, b should be passed to that method 
     (or that method creates b). 

[ a moment of silence while we think about relevant heuristics ]

 - 4.5 --> if a class contains objects, it should use them
 - 4.6 --> most of the methods should use most of the data most of the time
 - 4.7 --> don't contain too many things
 - 7.1 --> choose containment over association
 - 8.1 --> don't use global data to perform book-keeping
   - Jesse's conflicting heuristic: if lots of things share something, make it global 
  
Observation: You (We) have difficulty identifying heuristics that apply.
 - is that a problem with "the heuristic method" ?
 - is that a problem with "these heuristics" ?
   - Riel doesn't give us many useful heuristics for the stuff we've been asked
 - is that a problem with "something else" ?
   - we're newbies 
   - it's not very concrete (we haven't seen much code or many particular examples)

What is the benefit of reading Riel? 
 - the heuristics themselves
 - the problems these heuristics illustrate
 - the process of analysis in deciding which heuristics apply

Question:
 - How often should I apply Riel?
   - Riel's answer: You're not experienced.  Always apply my stuff.  You'll see...
   - Riel's followup: Experienced programmers always apply heuristics; they just know them well enough that they aren't always conscious of the application
   - in general, keep 'em in the back o' your mind.  and keep 'em handy during design