The Spirit of Refactoring

1
The Spirit of Refactoring

• Eric Allen
• Rice University

2
XP and Refactoring

• Collective code ownership enables refactoring
• Unit tests enable refactoring
• Non-fixed deadlines enable refactoring
• Pair programming enables refactoring

3
Perpetual Refactoring is Essential to a Projects
Continuation

• Not all code will be good code
• Project will never be in the ideal state (and
  even if it were, it wouldnt last long)
• Refactoring prevents code from collapsing under
  its own weight

4
Refactoring and Coding Standards

• Coding standards are arbitrary
• Discussing where to put braces is not science
• A common coding standard prevents waste of
  productivity

5
A Simple Refactoring

• public int i
• gt
• private final int i

6
Wont that break the code?

• No the type checker wont let it break
• If the type checker signals errors, you will get
  a list of all places in your code that youd have
  to fix to keep the refactoring
• Type checker as refactoring aid

7
Another Simple Refactoring

• public int VERYBADNAME
• gt
• public int muchBetterName

8
Can that break the code?

• Yes! Accidental shadowing is a problem
• public void m()
• int veryGoodName
• VERYBADNAME

9
Accidental Shadowing May Not Signal an Error

• public class C1
• int veryGoodName
• public class C2
• int VERYBADNAME
• veryGoodName

10
Unshadowing is Also a Problem

• public class C1
• int VERYBADNAME
• public class C2
• int VERYBADNAME
• VERYBADNAME

11
Automated Refactoring Tools

• Tools help ensure that the refactoring is done
  correctly (provided the tool is correct)
• IDEA has the fullest set of refactorings, but it
  only works for non-generic Java
• CodeGuide supports some refactorings

12
Extract Method

• public Object m()
• blah1
• blah2
• blah3
• blah4
• gt

13
Extract Method

• public Object m()
• m1()
• m2()
• public Object m1() blah1 blah2
• public Object m2() blah3 blah4

14
Other refactorings

• Make methods/classes/fields final (advantage?)
• Move methods into a superclass
• Push methods into subclasses
• What else?