CS 683 Emerging Technologies: Embracing Change Spring Semester, 2001 Extreme Programming Overview
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Extreme Programming (XP)

Four Variables of Software Development
The 12 Practices
What is Refactoring

Doc 13, Extreme Programming Overview Slide # 2

Extreme Programming (XP)

• Project to write a payroll system for Chrysler
• Project done in Smalltalk
• Kent Beck brought in to help an existing project

• Scrum
• Crystal Light
• Adaptive Software Development
• Dynamic System Development Method
• dX

• Light methods are adaptive rather than predictive

• Light methods are people-oriented rather than process-oriented.

Doc 13, Extreme Programming Overview Slide # 3

• Is a business
• Has risks

Schedules slip

Building the wrong product

Market for product changes

Buggy software

Too many features that users don't want

Struggle between management and developers

• Risks need to be managed

If can't manage risks than it is hard to succeed

Doc 13, Extreme Programming Overview Slide # 4

• You have the right to know what is needed, via clear requirements, with clear declarations of priority

• You have the right to say how long each requirement will take you to implement, and to revise estimates given experience

• You have the right to accept your responsibilities instead of having them assigned to you

• You have the right to produce quality work at all times

• You have the right to peace, fun, and productive and enjoyable work

Doc 13, Extreme Programming Overview Slide # 5

• You have the right to an overall plan, to know what can be accomplished, when and at what cost

• You have the right to see progress in a running system, proven to work by passing repeatable tests that you specify

• You have the right to change your mind, to substitute functionality, and to change priorities

• You have the right to be informed of schedule changes, in time to choose how to reduce scope to restore the original date. You can even cancel at any time and be left with a useful working system reflecting investment to date

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Four Variables of Software Development

• Cost

How much money to spend developing the product

Too little money makes it hard to develop the product

Too much money too soon causes problems

• Time

The time allocated to develop the product

Too little time makes development impossible

Too much time hurts development

Market may change

Lose feedback from system in use

• Quality

The least measurable variable

The first to suffer in a crunch

Poor quality increases development time and costs

• Scope

What features will be in the product

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The 12 Practices

• 40-hour work week
• Small Releases
• On-site Customer
• Pair Programming
• Continuous integration
• Testing
• Collective Ownership
• Coding Standards
• Simple design
• Metaphor
• Planning game
• Refactoring

Doc 13, Extreme Programming Overview Slide # 10

• Break story into small tasks
• Select the task they wish to work on

• Write tests for the task
• Write the code for the task
• Refactor to clean up design
• Integrate task into code base

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What is Refactoring

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            ifFalse: [(smallKey = anInteger)
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               ifFalse: [(anInteger < largeKey)
                  ifTrue: [self atMiddleTree: anInteger put: anObject]
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                     ifTrue: [largeValue := anObject]
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                        ifTrue: [self atRightTree: anInteger put: anObject]]]]]]
      ifFalse:
         [self addNewKey: anInteger with: anObject].

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      ifFalse: [^self addNewKey: anInteger with: anObject].
   anInteger < smallKey 
      ifTrue: [^self atLeftTree: anInteger put: anObject].
   smallKey = anInteger ifTrue: [^smallValue := anObject]
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      ifTrue: [^self atMiddleTree: anInteger put: anObject]
   largeKey = anInteger ifTrue: [^largeValue := anObject]
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      ifTrue: [^self atRightTree: anInteger put: anObject]

Doc 13, Extreme Programming Overview Slide # 13

• Replace Conditional with Polymorphism
• Introduce Null Object

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   aKey < smallData key ifTrue:[^leftSubtree at: aKey].
   aKey = smallData key ifTrue:[^smallData value].
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   aKey > largeData key ifTrue:[^rightSubtree at: aKey]
   
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   aKey = data key 
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      ifFalse:[self error: 'Key not found']
   
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   self error: 'Key not found'

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