Matthew Wagner

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Refactoring Improving Your Code

• Matthew Wagner
• Cs564
• Fall 2004

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Refactoring

• What is Refactoring?
• Where did this idea come from?
• When do we Refactor?
• How do we Refactor?
• Are there tools to help us Refactor?
• Why should we Refactor?
• Why might we not want to Refactor?
• What data has been accumulated on Refactoring?

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Refactoring Book Definition

• Refactoring is the process of changing a
  software system in such a way that it does not
  alter the external behavior of the code yet
  improves its internal structure. It is a
  disciplined way to clean up code that minimizes
  the chances of introducing bugs. In essence when
  you refactor you are improving the design of the
  code after it has been written.
• Refactoring Improving the Design of Existing
  CodeBy Martin Fowler, Kent Beck, John Brant,
  William Opdyke, Don Roberts

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Refactoring In Laymans Terms

• Make small changes to code to improve code
  structure, readability, and reusability.

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Refactoring Key Elements

• Simplifying complex statements
• Abstracting common solutions into reusable code
• Removal of duplicate code

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Short History

• Ward Cunningham and Kent Beck realize importance
  of Refactoring while working with Smalltalk in
  the 1980s.
• William Opdykes 1992 doctoral thesis explores
  the theoretical fundamentals for creating an
  automated tool to perform safe refactorings.
• In the late 90s John Brant and Don Roberts create
  the Refactoring Browser'' for the Smalltalk
  language.

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When to Refactor Smells in Code

• Refactor when the code smells.
• Smells are structures in the code that suggest
  the possibility of refactoring.
• http//wiki.java.net/bin/view/People/SmellsToRefac
  torings

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Examples of Code Smells

• Comments
• Can quickly become verbose and reduce code
  clarity.
• Long Method
• The longer the method the harder it is to see
  what its doing.
• Uncommunicative Name
• Middle Man
• A class is delegating almost everything to
  another class.

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Refactoring Methods

• Only refactor working code
• Refactorings should be Small
• Test often to avoid introducing bugs
• List of Refactorings
• http//www.refactoring.com/catalog

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Whats in a Refactoring?

• Name
• Summary
• Motivation
• Mechanics
• Examples

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Some Specific Refactorings

• Extract Method
• Use fragment to create method whose name explains
  the purpose of the method.
• Decompose Conditional
• Replace conditional logic with a method whose
  name explains its purpose
• Introduce Explaining Variable
• Put part of an expression in a temporary variable
  with a name that explains the purpose.
• Rename Member
• Change a name to be more descriptive.

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Extract Method

• Extract Method Use fragment to create method
  whose name explains the purpose of the method.

Before Extract Method Refactoring
After Extract Method Refactoring
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Decompose Conditional

• Decompose Conditional Replace conditional
  logic with a method whose name explains its
  purpose

Before Decompose Conditional Refactoring
After Decompose Conditional Refactoring
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Introduce Explaining Variable

• Introduce Explaining Variable Put part of an
  expression in a temporary variable with a name
  that explains the purpose.

Before Introduce Explaining Variable Refactoring
Int sizeToAllocate charSize
ds.Tables0.Rows0FirstName.ToString().Lengt
h
After Introduce Explaining Variable Refactoring
Int numChars ds.Tables0.Rows0FirstName.T
oString().Length Int sizeToAllocate charSize
numChars
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Rename Member

• Rename Member Change a name to be more
  descriptive.

Before Rename Member Refactoring
After Rename Member Refactoring
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Refactoring Tools

• Tool support makes refactoring faster and
  therefore more productive.
• Many feel that refactoring in not a feasible use
  of time without proper tool support.
• Most refactoring tools integrate into your
  favorite IDE.

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Refactoring Tools - CRefactory
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Why Refactor?

• Refactoring Improves the Design of Software
• Refactoring Makes Software Easier to Understand
• Source code is the best documentation
• Refactoring Helps You Find Bugs
• Refactoring Makes Software Easier to Change
• Refactoring Helps You Program Faster

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Problems with Refactoring

• Changing working code may introduce bugs
• Changing Interfaces or Names can have widespread
  effects
• Some design decisions are difficult to refactor
  later
• Databases can be hard to refactor
• Less immediate benefit as the deadline approaches
• Endless Refactoring How much is enough?

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Effectiveness of Refactoring

• The Effects of Individual Practices on Software
  Development Effort conducted at Pondicherry
  University, India
• Studied the effects of each of the 12 practices
  of Extreme Programming, of which Refactoring is
  one.

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Effectiveness of Refactoring
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Effectiveness of Refactoring

• The difference between no refactoring and
  refactoring
• as much as possible is only 30 developer-hours
• out of over 4000.
• This amounts to a 0.67 decrease in time spent,
• thanks to refactoring
• Is this enough to support Refactoring?

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Refactoring and Productivity

• Extreme Programming A Survey of Empirical Data
  from a Controlled Case Study, conducted at VTT
  Technical Centre of Finland

Productivity in Lines of Code per Hour and the
percent of Time spent refactoring during that
development period.
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References

• Refactoring Improving the Design of Existing
  CodeBy Martin Fowler, Kent Beck, John Brant,
  William Opdyke, Don Roberts
• www.refactoring.com
• www.extremeprogramming.org
• www.xtreme-simplicity.net
• http//wiki.java.net/bin/view/People/SmellsToRefac
  torings

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References (cont.)

• Abrahamsson, Pekka, et al. "Extreme Programming
  A Survey of Empirical Data from a Controlled Case
  Study." ACM-.IEEE International Symposium on
  Empirical Software Engineering (ISESE 2004).
  2004.
• S. Kuppuswami,et al. The Effects of Individual
  XP Practices on Software Development Effort.
  Pondicherry University Computer Science
  Department.