Defining RefactoringThe word Refactoring has two definitions

depending on context.Refactoring (noun): a change made to the

internal structure of software to make it easier to understand and cheaper to modify without changing its observable behavior.

Refactor (verb): to restructure software by applying a series of refactorings without changing its observable behavior.

Defining RefactoringThe purpose of refactoring is to make the software

easier to understand and modify.It only alters the internal structure.A good contrast is performance optimization.Refactoring does not change the observable

behavior of the software.

The Two HatsTwo distinct activities: adding function and

refactoring.When you add function, you shouldn't be changing

existing code; you are just adding new capabilities.When you refactor, you make a point of not adding

function; you only restructure the code.

Refactoring Improves the Design of SoftwareWithout refactoring, the design of the program will

decay.Poorly designed code usually takes more code to do

the same things.

Refactoring Makes Software Easier to UnderstandProgramming is in many ways a conversation with a

computer.There is another user of your source code.“I use refactoring to help me understand unfamiliar

code.I actually change the code to better reflect my

understanding.”

Refactoring Helps You Find BugsHelp in understanding the code also helps me spot

bugs."I'm not a great programmer; I'm just a good

programmer with great habits."

Refactoring Helps You Program FasterRefactoring helps you develop software more

rapidly, because it stops the design of the system from decaying.

When Should You Refactor?Refactor When You Add FunctionRefactor When You Need to Fix a BugRefactor As You Do a Code Review

What Do I Tell My Manager?If the manager is technically savvy, introducing

the subject may not be that hard.If the manager is genuinely quality oriented, then

the thing to stress is the quality aspects.Of course, many people say they are driven by

quality but are more driven by schedule. In these cases I give my more controversial advice: Don't tell!

DatabasesMost business applications are tightly coupled to the

database schema that supports them.The database is difficult to change.Another reason is data migration.

With nonobject databases, place a separate layer of software between your object model and your database model.

Object databases both help and hinder.

Changing InterfacesThere is no problem changing a method name if you

have access to all the code that calls that method.There is a problem only if the interface is being used

by code that you cannot find and change.Don't publish interfaces prematurely. Modify your

code ownership policies to smooth refactoring.

Design Changes That Are Difficult to RefactorHow difficult would it be to refactor from one design

into another?Pick the simplest design if it seems easy.Otherwise put more effort into the design.

Refactoring and DesignRefactoring can be an alternative to upfront design.In refactoring, you still do upfront design, but now

you don't try to find the solution. Instead all you want is a reasonable solution. You know that as you build the solution, as you understand more about the problem

An important result of this change in emphasis is a greater movement toward simplicity of design.

Refactoring and PerformanceA common concern with refactoring is the effect it

has on the performance of a program.Three general approaches to writing fast software:

time/footprint budget for resourcesconstant attention approachperformance improvement

Where Did Refactoring Come From?Two of the first people to recognize the importance

of refactoring were Ward Cunningham and Kent Beck, who worked with Smalltalk from the 1980s onward.