RefactoringCristescu 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

• As a verb: the activity of restructuring software by applying a series of refactorings without changing the observable behavior of that software

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

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

When should we Refactor?

• To add new functionality• To find bugs• For code reviews• For TDD (Test, Code, Refactor)

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

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

Common Code Smells

• Duplicated code• Feature Envy• Comments• Long Method• Long Parameter List• Switch Statements• Improper Naming

Some Refactorings

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.

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.

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;

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.

Rename Method

• The name of a method does not reveal its purpose.

• Change the name of the method.

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.

Pull Up Field

• Two subclasses have the same field.• Move the field to the superclass.

Separate Domain from Presentation

• You have GUI classes that contain domain logic.• Separate the domain logic into separate domain classes

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

Bibliography

• Martin Fowler: Refactoring: Improving the Design of Existing Code, Addison–Wesley.

• http://en.wikipedia.org/wiki/Database_refactoring