Week 2 Design Examples and Designing for Change

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Week 2Design Examples andDesigning for Change

• Alex Baker

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Implementation Design

• An implementation design is a road map
• understandable, unambiguous, consistent, helpful,
  
• An implementation design describes a path from
  system design to the outcome
• correct, complete, concise, verifiable,
  effective,
• An implementation design describes what the
  implementers should do
• elegant, partitionable, recomposable, resilient,
  
• An implementation design is a guide towards
  future change
• evolvable,

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Emphasis on Changability

• Change abounds
• During design
• During coding
• Upon delivery
• After use
• Reuse for later projects

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Emphasis Changability

• Subtle
• Requires foresight and careful balancing
• An implementation design describes what the
  implementers should do
• elegant, partitionable, recomposable, resilient,
  
• An implementation design is a guide towards
  future change
• evolvable,

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Changability Basic Principles

• Low Coupling Reducing interdependency
• Changes dont propagate
• Reuse is facilitated
• High Cohesion Grouping functionality
• Easier to find things
• Metaphor guides decisions
• Information Hiding

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The Ideal Program
vs.

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A Very Simple Example

• A sorted list class with
• getArray() Array
• getElementAt(int i) Element

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A Very Simple Example

• A List class with
• getArray() Array
• getElementAt(int i) Element
• Its too slow, so we switch to a hash table
• Everywhere you call getArray needs changing
• Only List is changed
• Little things like this add up

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UML Review Class Diagrams

• Class Name

Attribute Type
Attribute Type
Operation (parameter) Return Type
Operation (parameter) Return Type
Operation (parameter) Return Type
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UML Review Class Diagrams

• Association

Generalization
Aggregation
Composition
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A Class Diagram
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Example 1 Theseus and the Minotaur

• http//www.logicmazes.com/theseus.html

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Original Theseus Design
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Original Theseus Design

• What if we want to add Water ?

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Original Theseus Design

• What if we want to add Water ?

?
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Original Theseus Design

• What if we want to add Water ?
• How do we fix this?

?
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TntM Changes

• Changing the board size
• Adding terrain types
• Adding more monsters
• Adding a second player
• Intelligent elements

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TntM 2
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TntM 2 Object Interfaces Inheritance
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TntM Changes

• Changing the board size
• Adding terrain types
• Adding more monsters
• Adding a second player
• Intelligent elements

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How far is too far?

• Changing board size?
• Pushable blocks?
• Intelligent elements?
• Real time gameplay?
• Physics challenges?

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Bonus!

• StompOn( stompee )
• Or
• StompedOn( stomper )

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Example 2 Klax

• Blocks fall from above, use a paddle to catch
• Deposit blocks in one of 5 columns
• Try to make lines of 3 in a row or more
• http//www.123games.dk/game/puzzle/klax3d/klax_eng
  .php

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A Good Klax Design?
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Chiron 2 Architectural Style
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C2 Klax
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Spelling Klax?
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Spelling Klax?
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Scrabble?

• How did you design for change?

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Scrabble?

• How did you design for change?
• Could you redesign / refactor for
• Changes to letter values?

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Scrabble?

• How did you design for change?
• Could you redesign / refactor for
• Changes to letter values?
• Changes to bonus squares?

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Scrabble?

• How did you design for change?
• Could you redesign / refactor for
• Changes to letter values?
• Changes to bonus squares?
• AI opponents?

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Scrabble?

• How did you design for change?
• Could you redesign / refactor for
• Changes to letter values?
• Changes to bonus squares?
• AI opponents?
• Different dictionaries?

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Summary

• Designing for change is a matter of
• Controlling dependency
• Proper encapsulation
• Generalizing where you can
• More broadly, you are asking
• What are the biggest change risks?
• What kind of program is this, essentially?
• Where is the line?

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Assignment 1 Continued

• Well exchange designs now
• Review forms will be online tonight
• Send completed forms to Andre and I
• abaker_at_ics.uci.edu
• andre_at_ics.uci.edu
• Due 600 pm, Sunday