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priscilla-shaw

Refactoring - PowerPoint PPT Presentation

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Refactoring
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  1. Refactoring

  2. http://c2.com/cgi/wiki?ExtremeNormalForm • Your classes are small and your methods are small; you've said everything OnceAndOnlyOnce and you've removed the last piece of unnecessary code. • Somewhere far away an Aikido master stands in a quiet room. He is centered.. aware.. ready for anything. • Outside a sprinter shakes out her legs and settles into the block, waiting for the crack of the gun while a cool wind arches across the track. • Softly, a bell sounds.. all of your tests have passed. • Your code is in ExtremeNormalForm.. tuned to today and poised to strike at tomorrow.

  3. Refactoring • Changes made to a program that only change its organization, not its function. • Behavior preserving program transformations.

  4. Why refactoring is important • Only defense against software decay. • Often needed to fix reusability bugs. • Lets you add patterns after you have written a program; lets you transform program into framework. • Lets you worry about generality tomorrow; just get it working today. • Necessary for beautiful software.

  5. Piecemeal Growth • The way living things grow • The way software grows • More than just addition -- transformation

  6. Duplicate code • Eliminate duplication by • making new methods • making new objects • moving methods to common superclass

  7. Long methods • Each method should do one thing. • One comment for each method. • Method should fit on the screen. • Method is all on same level of abstraction. • Method should be in right class.

  8. Move code to its right class • teacher classes add: thisClass. • teacher classLoad: (teacher classLoad + 1) • teacher addClass: thisClass

  9. Large classes • More than seven or eight variables • More than fifty methods • You probably need to break up the class • Components (Strategy, Composite, Decorator) • Inheritance

  10. Long parameter lists • If you see the same set of parameters repeated in several methods, bundle them into a new object. Create accessors to get the original parameters from the object. Change the methods to use the new object instead of the parameters. • Then figure out what other funtionality needs to move to the object.

  11. Case Statements • Use polymorphism, not case statement. • Make class hierarchy, one class for each case. • Make a method for each case statement. • Make each branch of case statement be a method in a class

  12. How to refactor • Make changes as small as possible. • Test after each change. • Many small changes are easier than one big change. • Each change makes it easier to see that more changes are needed.

  13. Refactoring browser • A better browser • Automates many refactorings - renaming, moving code, splitting • Undo • Smalllint tool helps you find places that need to be refactored.

  14. When to refactor • If a new feature seems hard to implement, refactor. • If a new feature created some ugly code, refactor. • When you can’t stand to look at your code, refactor.