Frogs design
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** 5.1 [[Inheritance for specialization]]: A toad is not a frog; it's [[Avoid_inheritance_for_implementation|inheritance for implementation]]. | ** 5.1 [[Inheritance for specialization]]: A toad is not a frog; it's [[Avoid_inheritance_for_implementation|inheritance for implementation]]. | ||
** 5.17 [[Avoid no-op overrides]]: The ''hop'' and ''swim'' methods of ''Egg'' do nothing. | ** 5.17 [[Avoid no-op overrides]]: The ''hop'' and ''swim'' methods of ''Egg'' do nothing. | ||
| + | ** 5.12 [[Beware type switches]]: ''Frog'' has a type attribute which is used in ''swim()'' (5.13 as well?) | ||
* The biologist should have the saute method, not the frog itself. | * The biologist should have the saute method, not the frog itself. | ||
Revision as of 03:02, 20 July 2009
An OO model of frogs. This beautiful design appeared in the 2004 427 exam.
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.
Broken heuristics
- Riel's heuristics
- 2.1 Hide data within its class: The AdultFrog class exposes an array of eggs it has laid.
- 2.9 Keep related data and behavior in one place: Frog and FrogBrain are separate classes.
- 3.5 Interface should be dependent on model: The Move interface contains a method called display; the model is dependent on the interface
- 3.9 Avoid verb classes: The Move interface is a verb. It could be called Movable or similar (although that name is still not great for other reasons).
- 3.10 Agent classes irrelevant: The Biologist class is an agent.
- 5.14 Avoid becomes: A frog will at various stages be an egg, tadpole and adult frog.
- Solution: State or strategy pattern
- 5.1 Inheritance for specialization: A toad is not a frog; it's inheritance for implementation.
- 5.17 Avoid no-op overrides: The hop and swim methods of Egg do nothing.
- 5.12 Beware type switches: Frog has a type attribute which is used in swim() (5.13 as well?)
- The biologist should have the saute method, not the frog itself.
