Frogs design
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* [[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. | * [[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. | ||
| − | :''This is a good start, but needs | + | :''This is a good start, but needs more explanation of how the rules are broken here. Also needs a note about this contribution on the discussion page. --[[User:Warwick Irwin|Wal]]'' |
== "Feels Bad" == | == "Feels Bad" == | ||
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* ''Toad'' is a subclass of ''AdultFrog''. | * ''Toad'' is a subclass of ''AdultFrog''. | ||
* ''FrogBrain'' contains an array of ''Egg'' | * ''FrogBrain'' contains an array of ''Egg'' | ||
| + | |||
| + | :''Why do these things feel bad? --[[User:Warwick Irwin|Wal]]'' | ||
Revision as of 01:34, 23 July 2008
An OO model of frogs. This beautiful design appeared in the 2004 427 exam.
Contents |
Design notes
- This design models the lifecycles of Frogs.
- A Frog begins life as an Egg, grows into a Tadpole and then an AdultFrog.
- A FrogBrain belongs to a Frog and manages its behaviour.
- There is one Biologist, Igor, who sometimes moves Frogs around. Igor has been known to fry their legs in white wine.
- Toads don’t have the same lifecycle as Frogs, but they look and act a lot like Frogs.
- Toads eat AdultFrogs.
Design Critique
This design is perfect. It cannot be faulted.
Broken heuristics
- Beware type switches - Frog phases: Egg, Tadpole, AdultFrog.
- Beware value switches - Tadpole
- 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.
- This is a good start, but needs more explanation of how the rules are broken here. Also needs a note about this contribution on the discussion page. --Wal
"Feels Bad"
- Toad is a subclass of AdultFrog.
- FrogBrain contains an array of Egg
- Why do these things feel bad? --Wal
