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Refactoring

Refactoring. Cristescu Marilena. Definitions. Loose Usage: Reorganize a program(or something) As a noun: a change made to the internal structure of some software to make it easier to understand and cheaper to modify, without changing the observable behavior of that software

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Refactoring

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  1. Refactoring Cristescu Marilena

  2. Definitions • Loose Usage: Reorganize a program(or something) • As a noun: a change made to the internal structure of some software to make it easier to understand and cheaper to modify, without changing the observable behavior of that software • As a verb: the activity of restructuring software by applying a series of refactorings without changing the observable behavior of that software

  3. What is Refactoring? • A series of small steps, each of which changes the program’s internal structure without changing its external behavior – Martin Fowler • Verify no change in external behavior by: • Testing • Using the right tool – IDE • Formal code analysis by tool • Being very, very careful

  4. Why do we Refactor? • Helps us deliver more business value faster • Improves the design of our software: • Easier to maintain and understand • Easier to facilitate change • More flexibility • Increase re-usability • Minimizes technical dept • Keep development at speed • To make the software easier to understand • To help find bugs • To “Fix broken windows” – Pragmatic Programmers

  5. When should we Refactor? • To add new functionality • To find bugs • For code reviews • For TDD (Test, Code, Refactor)

  6. Team Techniques • Encourage refactoring culture • Nobody gets things right the first time • Nobody can write clear code without reviews • Refactoring is progress • Provide sound testing base • Tests are essential for refactoring • Build system and run tests daily • Pair Programming • Two programmers working together can be quicker than working separately • Refactor with the class writer and a class user

  7. How do we Refactor? • We look for Code-Smells • Things that we suspect are not quite right or cause us severe pain if we do not fix

  8. Common Code Smells • Duplicated code • Feature Envy • Comments • Long Method • Long Parameter List • Switch Statements • Improper Naming

  9. Some Refactorings

  10. Move Method • A method is, or will be, using or used by more features of another class than the class on which it is defined. • Create a new method with a similar body in the class it uses most. Either turn the old method into a simple delegation, or remove it altogether.

  11. Extract Class • You have one class doing work that should be done by two. • Create a new class and move the relevant fields and methods from the old class into the new class.

  12. Replace Magic Number with Symbolic Constant • You have a literal number with a particular meaning. • Create a constant, name it after the meaning, and replace the number with it.. double potentialEnergy(double mass, double height) { return mass * 9.81 * height; } double potentialEnergy(double mass, double height) { return mass * GRAVITATIONAL_CONSTANT * height; } static final double GRAVITATIONAL_CONSTANT = 9.81;

  13. Replace Subclass with Fields • You have subclasses that vary only in methods that return constant data. • Change the methods to superclass fields and eliminate the subclasses.

  14. Rename Method • The name of a method does not reveal its purpose. • Change the name of the method.

  15. Parameterize Method • Several methods do similar things but with different values contained in the method body. • Create one method that uses a parameter for the different values.

  16. Pull Up Field • Two subclasses have the same field. • Move the field to the superclass.

  17. Separate Domain from Presentation • You have GUI classes that contain domain logic. • Separate the domain logic into separate domain classes

  18. Database Refactoring • A database refactoring is a simple change to a database schema that improves its design while retaining both its behavioral and informational semantics • Database Smells: • stored code: Monster Procedures, Spaghetti, Duplication, IF-ELSE overuse, low cohesion • Database schema: Multi-purpose table / column, Redundant data, Tables with many columns / rows, Lack of constraints

  19. Bibliography • Martin Fowler: Refactoring: Improving the Design of Existing Code, Addison–Wesley. • http://en.wikipedia.org/wiki/Database_refactoring

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