4. Design and The Count

• Design Road Map
• http://www.gvu.gatech.edu/edtech/BOOST/designmap.html
• How To Design
• Analysis
• Identifying Candidate Classes
• Choosing from Candidate Classes
• Assigning Responsibilities
• Design
• Assigning Attributes and Services
• Assigning Services
• Assigning Links
• Inheritance
• Composition
• Broadcast
• The Count
• Pieces:
• Introducing the Problem
• OOA: Object-Oriented Analysis
• OOD: Object-Oriented Design
• OOP: Object-Oriented Programming
• Why we did it so flexibly: ASCII and Date Counts
• Why we aimed for reuse: A Profit Calculator
• Introducing the Problem
• I love to count. Build me a system to help with that counting.
• I want to know how much I have counted. And I want to increment and decrement the counter.
• I had a bright red plastic counter.
• 
• OOA: Object-Oriented Analysis
• What classes?
• What are the relationships between classes?
• What are the services and attributes of each?
• Goals:
• Aim for flexibility
• Aim for reusability
• OOA: What do we need?
• Nouns: Count(er)
• Services: incrementing, decrementing, reseting
• Attributes: value, resetValue
• 
• OOA: Flexibility
• What if we want to count Integers in other bases?
• 
• OOA: Flexibility and Reusability
• What if we want to count dates? sequences? letters?
• 
• Note:
• Abstract Classes: Never create instances. Shared functionality only.
• Concrete Classes: Create instances
• OOD: Object-Oriented Design
• What do the services->methods do?
• Increment, Decrement, Reset
• Fill in the details
• Accessing instance variables
• Initializations
• OOP: Object-Oriented Programming
• Create the Count Class Definition
• Model subclass: #Count
• instanceVariableNames: 'value resetValue '
• classVariableNames: ''
• poolDictionaries: ''
• category: 'Counts'
• OOP: Accessing
• Count methodsFor: 'accessing'
• value
• "Return my value"
• ^value
• value: aValue
• value := aValue
• resetValue
• ^resetValue
• resetValue: aValue
• resetValue := aValue
• OOP: Counting Methods
• Count methodsFor: 'counting'
• decrement
• "Subclasses must implement"
• self subclassResponsibility
• increment
• "Subclasses must implement"
• self subclassResponsibility
• reset
• value := resetValue
• OOP: Initialization
• Count methodsFor: 'initialization'
• initialize
• self reset
• Count class methodsFor: 'initialization'
• new
• | aCount |
• aCount := super new.
• aCount initialize.
• ^aCount
• Now, Creating the IntegerCount
• Count subclass: #IntegerCount
• instanceVariableNames: ''
• classVariableNames: ''
• poolDictionaries: ''
• category: 'Counts'
• IntegerCount methodsFor: 'counting'
• increment
• value := value + 1.
• decrement
• value := value - 1.
• asBase: radix
• ^value printStringBase: radix "printStringRadix: in VisualWorks"
• Finishing up IntegerCount
• IntegerCount methodsFor: 'initialization'
• initialize
• resetValue := 0.
• super initialize.
• Testing
• | aCount |
• aCount := IntegerCount new.
• aCount value: 10.
• Transcript cr; show: 'Current Value; ', aCount value printString.
• aCount increment. aCount increment.
• Transcript cr; show: 'Current Value: ', aCount value printString.
• aCount decrement.
• Transcript cr; show: 'Current Value: ', aCount value printString.
• aCount reset.
• Transcript cr; show: 'Current Value: ', aCount value printString.
• Testing Flexibility: Creating a DateCount
• 
• Count subclass: #DateCount
• instanceVariableNames: ''
• classVariableNames: ''
• poolDictionaries: ''
• category: 'Counts'
• DateCount methodsFor: 'counting'
• decrement
• value := value subtractDays: 1.
• increment
• value := value addDays: 1.
• initialize
• resetValue := Date today.
• super initialize.
• Testing Reuse: Profit Calculation
• Imagine a counter at a gate (Airport, Six Flags)
• Profit is some percentage of the gate
• 
• Question: Just talks-to or has-a?
• OOP: Profit
• Object subclass: #Profit
• instanceVariableNames: 'gateCount margin ' "Fixed it from the picture"
• classVariableNames: ''
• poolDictionaries: ''
• category: 'Counts' "Probably shouldn't be this"
• Profit methodsFor: 'calculate'
• initialize: aCount
• gateCount := aCount.
• margin := 0.25.
• total
• ^ margin * (gateCount value).
• Profit testing
• | profit aCount |
• profit := Profit new.
• aCount := IntegerCount new.
• profit initialize: aCount.
• 10 timesRepeat: [aCount increment].
• Transcript cr; show: 'Profit so-far: ', profit total printString.