CSC223 2004F, Class 32: Choosing and Using Heuristics

Admin:
* Scumbags stole projector in 2435 and cable from here
* Ryan is sick; Kat is just missing; Gene's alarm probably didn't work
* No alum talk today!
* Math/CS lunch today!
* Friday's positives
  * Everybody enthusiastic about presenting
  * Presenting groups did a good job
  * Good interfaces
  * Cats!
* Friday's negatives
  * YOU SHOULD REMEMBER STUFF FROM CLASS TO CLASS!
    * Subject
    * General details
  * YOU SHOULD BE ABLE TO SYNTHESIZE THE STUFF YOU'VE FORGOTTEN (or never learned)!
* Assignments for today:
  * Finish chapters 4 through 7
  * Try to decide which heuristics apply to the choice of relationships and ways to obtain usable objects
QUIZ:
* Subject: "CS223: Sam is upset"
  * Why did you not bother to figure out what the homework was for today?
  * Why did you not do the homework for today?
  * What can I do to give you more incentive to do the work?
  * Anything related

Overview:
* How today's class works
* Choosing a relationship
* Choosing how to get objects to use

/Choosing a Relationship Classes and Objects/

* Use
* Contain
  * Directly
  * Via association
* Extend
* Associate
  * Contain
  * Create
  * Other (default)

/Choosing an Object/

* The ways in which an object obtains other objects to use
  * Passed as a parameter to a method call
  * Contain that object
  * Contain a reference to that object
  * Create the object ("rich person's solution")
  * Ask an oracle for the object
  * Use a global object
  * Pass the request to an oracle for forwarding

HOW DO WE MAKE THE CHOICE OF WHICH WAY SAM GETS A PEN?
* First answer: Heuristics
* Kat's first heuristic: If the object is used in only one method, you should either (1) receive it as a parameter or (2) create it yourself

Notes from Evan Case:

Relationship Choices

Riel:

- 4.14: Objects that share lexical scope should not have *uses* relationships between them.
        -> used by containing class
        ex. ATM: card reader should pass error to ATM and let ATM deal with it rather than ask the ATM for the screen and then talk to the screen directly.


[Def'n: "Scope" - limitiation on the visibility/accessibility of a variable or object -- two big ways to limit scope:
        Lexical/Static: look at the words
        Dynamic: Look at the execution

]


- 4.13: A class must know what it contains, but it should never know who contains it.
        -> Doesn't help us pick which relationship to choose?


So, how do we choose a relationship?

In 4.14, it should be *any* relationship, not just *uses*...

- 7.1: When given a choice in an object-oriented design between a containment relationship and an association relationship, choose the containment relationship.

        -> "association containment" vs. "pure containment", choose "pure containment"

        why this is important:
        - models the real world better.
                auto 1 ------> 1 manufacturer

7.1, rephrased: if you have a 1-1 relationship between class A and B and are making a choice between containment and association, use containment. 

5.1: (as stated by TangSam) Use inheritance when there is a hierarchical relationship.

ex. Grinnell^H "Traditional Company"

Pres

VP VP VP VP

Section Heads

Team Leaders

Peons

So this is a hierarchy, but there wouldn't be inheritance.


OOPS: 5.1 really is: "Inheritance should only be used to model a specialization hierarchy."

MORAL: Be careful about using your own language.

/Detour: Stupid Jokes/

"Is 'anal retentative' hyphenated."

As the object of a verb, as in "Sam is anal retentive.": no
As adjective, as in "Sam is an anal-retentive grader.": yes