Object/Class Design Slides adapted from Craig Zilles 1 Design is - - PowerPoint PPT Presentation

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Object/Class Design Slides adapted from Craig Zilles 1 Design is - - PowerPoint PPT Presentation

Apr 13, 2023 249 likes •417 views

Object/Class Design Slides adapted from Craig Zilles 1 Design is hard Design is an art, not a science Large/infinite design space, not enumerable Requirements, constraints, trade-offs, and priorities You get better with practice /

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Object/Class Design

Slides adapted from Craig Zilles

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Design is hard

¢ Design is an art, not a science ¢ Large/infinite design space, not enumerable ¢ Requirements, constraints, trade-offs, and priorities ¢ You get better with practice / experience / seeing good

design / hearing critiques of others designs

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Virtues of a good design (software)

¢ Manages complexity ¢ Loose coupling ¢ Reusability ¢ Ease of maintenance ¢ Standard techniques ¢ Extensibility ¢ Lots of Uses ¢ Few Dependencies

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Good Design Manages Complexity

¢ “Seven plus or minus two” (Miller’s Law) ¢ The goal of all software-design techniques

§ Break complicated problems into simple problems

¢ Separation of concerns

§ Focus on one at a time

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Keep Coupling Loose

¢ small interfaces (few methods, few arguments/method) ¢ obvious (interactions through parameter passing) ¢ flexible

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How hard was third code review assignment?

A) Easy B) Moderate C) Challenging D) Unreasonable

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How long did third assignment take?

A) Less than 3 hours B) 3 to 6 hours C) 6 to 9 hours D) 9 to 12 hours E) More than 12 hours

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Abstract Data Types

¢ Define a class based around conceptual structures

§ Encapsulation / information-hiding § Make interfaces more informative (self-documenting) § Easier to reason about correctness

¢ Treat even simple items as ADTs

§ Good for extensibility

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Java Collection Framework

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Map

¢ Allows lookups from one kind of object to find another

  • bject

Map<KeyType, ValueType> myMap = HashMap<KeyType, ValueType>(); KeyType key = …; ValueType value = …; myMap.put(key, value); ValueType lookup = myMap.get(key); assert lookup == value;

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Map Interface

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put(k,v) Associate v with k

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get(k) The value associated with k

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size() The number of pairs

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isEmpty() Whether it is empty

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remove(k) Remove the mapping for k

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clear() Remove all mappings

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containsKey(k) Whether contains a mapping for k

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containsValue(v) Whether contains a mapping to v

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keySet() Returns the Set view of keys

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entySet() Returns the Set view of keys and values

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Inheritance can provides 2 things

¢ Shared interface:

§ Public methods § Ensure methods have consistent meaning in derived class

§ Liskov Substitution Principle

¢ Shared implementation

§ Code in shared super class, not replicated in each derived § Could be private data/methods

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hasA vs. isA relationship

Which is a candidate for inheritance? A) hasA relationship B) isA relationship C) both hasA and isA relationships D) neither hasA and isA relationships

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Inheritance vs. Interfaces

¢ Inheritance should be a isA relationship ¢ Interfaces are for capabilities (“mixin”s)

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Designing Good Interfaces

¢ Sufficiently Expressive ¢ General ¢ Minimal