Refactoring
An Introduction
Giorgio Vespucci

“Software must be soft: it
has to be easy to change
because it will change
despite our misguided
efforts otherwise.”
The Pragmatic Programmers

What we want
Robustness
Simplicity
Softness

What we see
Fragility
Complexity
Rigidity

Unreadable
code is…

Hard to modify

Duplicated
code is…

Hard to modify

Complex
code is…

Hard to modify

Refactored
code is...

Easier to
understand

Cheaper
to modify

Clean
code

Better
code

Refactored
code shows...

Changes to its
internal structure

But no change to
observable behavior

“So what?”

Try to understand
this Java code

java.util.Calendar c =
java.util.Calendar.getInstance();
c.set(2005, java.util.Calendar.NOVEMBER, 20);
c.getTime();

Uhm... a Date...

And now this code

october(23,2008);

Hey, mum! It's a Date!

“Any fool
can write code
that a computer
can understand.”

“Good programmers write
code
that humans
can understand.”
Martin Fowler - Refactoring

What do we
need ?

“If you want to refactor, the essential
precondition is having solid tests.”
Martin Fowler - Refactoring

Measures matter

Where to start ?

Look at
the code

Sniff
the code

Does it smell ?

Duupliccateed code?
Loooooong method?
L a r g e class?

The Refactoring cycle
1) Choose the worst smell
2) Select a refactoring
3) Apply the refactoring
4) Run all the tests

little steps

Great
results

Must-have books on Refactoring
Refactoring: Improving the Design of Existing
Code
(Addison-Wesley Object Technology Series)
Martin Fowler
Refactoring Workbook
(Addison-Wesley Object Technology Series)
William C. Wake
Refactoring to Patterns
(Addison-Wesley Signature Series)
Joshua Kerievsky

Online resources
Smells to refactor
http://wiki.java.net/bin/view/People/SmellsToRefactorings
Alpha list of refactoring
http://www.refactoring.com/catalog/index.html
Refactoring Workbook Website
http://xp123.com/rwb/
Refactoring to Patterns catalog
http://industriallogic.com/xp/refactoring/catalog.html