Refactoring

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Refactoring

• Presented by Jason Lee

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Overview

• Defining Refactoring
• Justification
• Methodologies and Best Practices
• Examples
• Future Work
• Questions

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What is Refactoring?

• Code reorganization
• Implies equivalence
• Change the structure, not the behavior
• Example (x2-1) (x1)(x-1)
• Cleans up messy code
• Does NOT fix bugs

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Refactoring and XP

• XP uses extreme levels of good programming
  practices
• The core practices of XP
• Pair programming
• Refactoring
• Testing
• Continuous integration
• Evolutionary design

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Costs and Benefits

• Costs
• Resource overhead
• Requires experience
• Benefits
• Improves understandability
• Simplifies testing
• Uncovers bugs
• "The two most important tools an architect has
  are the eraser in the drawing room and the sledge
  hammer on the construction site."
• Frank Lloyd Wright

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How do we refactor?

• Manual Refactoring
• Code Smells
• Automated/Assisted Refactoring
• Refactoring by hand is time consuming and prone
  to error
• Eclipse (www.eclipse.org)
• .NET Refactoring (www.dotnetrefactoring.com)
• In either case, test your changes

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Code Smells

• A hint that something is wrong
• Detection comes with experience
• Table of common smells
• http//wiki.java.net/bin/view/People/SmellsToRefac
  torings

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Code Smell Examples

• Too much code
• Methods that are too big
• Duplicated code
• Code that is not executed
• Not enough code
• Classes with little code
• Empty catch clauses
• Outside the code
• Excessive logging
• Excessive commenting

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Best Practices

• Refactor in small steps
• Do not change interface and implementation
  simultaneously
• Minimize sources of error
• Test continuously
• Refactor with a purpose

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Refactoring Examples

• Renaming methods and variables
• Extracting methods
• Replace conditionals with polymorphism
• Hide implementation with interface

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Example 1Expansion and Contraction

• Gray bars denote duplicated code

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Example 2Collapsing Hierarchy

• Centralize related behavior into single class

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Example 3Indirection

• Removes direct dependency of client code from the
  feature

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Future Work

• Refactoring noses
• Refactoring SE artifacts
• Inclusion into classical models of SE
• Scalable refactoring

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Summary

• Refactoring does not affect behavior
• Gaining experience and confidence is necessary
• Use tools to reduce errors
• Each behavior should do all of one thing, do one
  thing well, and do only one thing

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References

• 1 Smith, Suzanne, and Stoecklin, Sara. What We
  Can Learn from Extreme Programming. Consortium
  for Computing in Small Colleges, 2001.
• 2 Fowler, Martin. Refactoring. ICSE 02, May
  19-25, 2002.
• 3 Fowler, Martin. Refactoring Home Page.
  www.refactoring.com
• 4 Mens, Tom, et al. Refactoring Current
  Research and Future Trends. LDTA 03 Preliminary
  Version, 2003.
• 5 Wikipedia Refactoring. http//en.wikipedia.or
  g/wiki/Refactoring
• 6 Wiki Pages about Refactoring.
  http//c2.com/cgi/wiki?WikiPagesAboutRefactoring

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Questions
?