Lecture sequence
| Line 27: | Line 27: | ||
''Woo hoo! Award for bravery to [[User:Jason Clutterbuck]]. --[[User:Warwick Irwin|Wal]] 23:45, 17 July 2008 (UTC)'' | ''Woo hoo! Award for bravery to [[User:Jason Clutterbuck]]. --[[User:Warwick Irwin|Wal]] 23:45, 17 July 2008 (UTC)'' | ||
| + | |||
| + | == Week 2 == | ||
| + | |||
| + | The [[Frogs design]] appeared, and it was beautiful. | ||
| + | |||
| + | Or was it? Slowly, painfully, the latent forces of evil were teased out. As [User:Yugan Yugaraja]] put it: | ||
| + | * [[Avoid becomes]] - ''Frog'' phases of life are modeled by inheritance: ''Egg'' ''Tadpole'', ''AdultFrog''. | ||
| + | * [[Beware type switches]] - the ''phase'' variable in ''Frog'' is based on the type of an object (''Frog''). | ||
| + | * [[Beware value switches]] - the ''swim()'' method in ''Tadpole'' differs in behavior based on the value of an attribute (''type''). | ||
| + | * [[Avoid no-op overrides]] ("Design by Contract") - the derived class ''Egg'' overrides the base class's ''hop()'' and ''swim()'' methods with methods which does nothing. | ||
| + | * [[One key abstraction]] - the ''Move'' interface contains more than one key abstraction. It contains methods to move such as ''hop()'' and ''swim()'', but it also contains a ''display()'' method which is a separate key abstraction. | ||
| + | |||
| + | Badness was detected in the following two features, but the reasons remained unclear: | ||
| + | * ''Toad'' is a subclass of ''AdultFrog''. | ||
| + | * ''FrogBrain'' contains an array of ''Egg''. | ||
| + | |||
| + | And we didn't even get to find out how confused we were by the question: | ||
| + | * Should a ''Frog'' be able to export itself? | ||
| + | |||
| + | But then, lurching violently in a different direction, we trued to make a [[427 design standard]] but primarily managed to make [[Getters and setters]] look more confusing than they did before. The [[Encapsulation boundary]] problem was the cause of the grief. | ||
Revision as of 04:40, 25 July 2008
Week 1
"Blah blah blah" said User:Warwick Irwin. Nobody else got to say much. Some wiki pages were mentioned, including:
A big pile of books was waved threateningly at the students.
Everybody was asked to set up an account using their Real name.
Suddenly, it was Wednesday and everything changed. The Video rental system design example appeared, and students huddled into groups to scribble unintelligible marks on scraps of paper. Some of these scribbles were copied to the whiteboard, where they remained unintelligible. Several incantations were uttered:
- Separation of concerns
- Many to many association idiom
- Type and instance idiom (Couldn't think of a better name.)
- Beware type switches
- Switch statements smell
- Avoid redundant data
Learning happened, it seems.
A brave student (or students) should now update the Video rental system page with a record of the design(s) that emerged, & what we observed about it. Have courage.
Woo hoo! Award for bravery to User:Jason Clutterbuck. --Wal 23:45, 17 July 2008 (UTC)
Week 2
The Frogs design appeared, and it was beautiful.
Or was it? Slowly, painfully, the latent forces of evil were teased out. As [User:Yugan Yugaraja]] put it:
- Avoid becomes - Frog phases of life are modeled by inheritance: Egg Tadpole, AdultFrog.
- Beware type switches - the phase variable in Frog is based on the type of an object (Frog).
- Beware value switches - the swim() method in Tadpole differs in behavior based on the value of an attribute (type).
- Avoid no-op overrides ("Design by Contract") - the derived class Egg overrides the base class's hop() and swim() methods with methods which does nothing.
- One key abstraction - the Move interface contains more than one key abstraction. It contains methods to move such as hop() and swim(), but it also contains a display() method which is a separate key abstraction.
Badness was detected in the following two features, but the reasons remained unclear:
- Toad is a subclass of AdultFrog.
- FrogBrain contains an array of Egg.
And we didn't even get to find out how confused we were by the question:
- Should a Frog be able to export itself?
But then, lurching violently in a different direction, we trued to make a 427 design standard but primarily managed to make Getters and setters look more confusing than they did before. The Encapsulation boundary problem was the cause of the grief.
