SYSC2101 ObjectOriented Programming and Design Laboratory

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SYSC-2101 Object-Oriented Programming and Design
Laboratory

• Refactoring
• revised Jan 25th, 2004

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What is Refactoring?

• A refactoring is a change to a program that only
  affects the way it is organized, not its
  behavior (Ralph Johnson). Also called behavior
  preserving transformations.
• In general, refactoring is modifying the code
  base to ensure that each thing is done once and
  only once. If something is done multiple times,
  each of those times should be replaced by a call
  to the one routine that does the thing well and
  doesn't do anything else. If closely related
  things are done at places scattered throughout
  the code base, they should be pulled together
  into a single routine. (William Grosso)

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Why Refactor?

• Refactoring is the process of taking an object
  design and rearranging it in various ways to make
  the design more flexible and/or reusable. (Kyle
  Brown)
• efficiency, maintainability
• your understanding of the code and design
  improves
• your code improves!

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When to Refactor?

• whenever your code smells!
• typically when you find duplication in your code
• after you have finished writing code that just
  works
• before adding new functionality
• your code must still pass all tests after each
  refactoring!!!

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Refactoring Examples

• Add/remove parameter
• Change reference to value (or the other way
  around)
• not only a C issue! see immutable objects
• Consolidate conditional expression, decompose
  conditional
• Encapsulate collection, downcast, field
• Extract class, interface (Eclipse supports it!),
  method, subclass, superclass
• Form template method (very interesting!)
• Introduce parameter object
• Move/pull up/push down field, method (Eclipse
  supported!)
• Replace conditional with polymorphism
• Replace constructor with factory method
• Replace inheritance with delegation

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Resources

• Refactoring Improving the Design of Existing
  Codeby Martin Fowler
• http//www.refactoring.com
• complete catalog available at
• http//www.refactoring.com/catalog/index.html