CSC/ECE 517 Fall 2009/wiki 1a 9b SJ

What is Code Refactoring

According to the famous book "Refactoring: Improving the Design of Existing Code " by Martin Fowler: [5], refactoring is the process of applying behavior-preserving transformations to a program with the objective of improving the program’s design. Intuitively people refer to code refactoring as "cleaning it up."

Motivation of Refactoring

Refactoring is very useful for software engineer to maintain the quality of their code in different environment. In fact, no software can be guaranteed to be perfect when it is first developed. Usually when the source code is applied to different customer needs, we want to improve the inner-structure without modify the external behavior. The ability to refactor your code takes the pressure off the design phase of software development. Refactoring gives you the ability to change the design of the code at a later stage. This means that you don’t have to get the design absolutely right before you write any code. You can get a rough design worked out, code it up and then if (when) you spot a better design you can refactor your code towards the better design.

List of Common Refactorings

In the following we list some popular refactoring to specify how refactoring transform the code. For more detail information, the reader please refer to the section 2.1.2 of the thesis of Thomas Corbat [1]. [1] provide Ruby example for each refactoring this list.

1. Merge Class Parts

2. Convert Local Variable to Field

3. Encapsulate Field

4. Extract Method

5. Inline Class

6. Inline Method

7. Move Field

8. Move Method

9. Rename Class

10. Rename Field

11. Rename Local Variable

12. Rename Method

13. Replace Temporary Variable with Query

14. Split Temporary Variable

Ruby Example of Refactoring

• Before Rename:

def badRenameMethod
    puts("Hello World");
end

• After Rename:

def hello
    puts("Hello World");
end

• Before Encapsulation:

class SomeClass
    def initialize
        @field = 0;
    end
end

• After Encapsulation:

class SomeClass                
    def initialize
        @field = 0;
    end
    def field
        @field
    end
    private :field
    def field= field
        @field = field
    end
    private :field=
end
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Refactoring support for Current Ruby IDE
This the following table we summary the current ruby IDE and their refactoring support situation. 


Current Ruby IDE
Refactoring Support (Y/N)


ActiveState Komodo
N


NetBeans
N


Arachno Ruby
N


FreeRIDE
N


Mondrian Ruby IDE
N


Ruby in Steel
N


RubyMine
Y


Eclipse (Aptana)
Y


Example of Using Ruby Refactoring Tools in Eclipse
Here the renaming of the method "badRenameMethod" to "Hello" is illustrated for Ruby.  The source code is shown in section 1.3.


Here the encapsulation of the field "field" is illustrated for Ruby.  The source code is show in section 1.3.


Example of Using Java Refactoring Tools in Eclipse
Here the renaming of the method "badRenameMethod" to "Hello" is illustrated for Java. The source code is show in section 1.4. 


Here the encapsulation of the field "field" is illustrated for Java. The source code is show in section 1.4.
 


Comparison of Ruby and Java Refactoring Tools
Comprehensiveness
These are the following refactoring options available in eclipse for Ruby and Java.



Refactoring Options for Java in Eclipse

Refactoring Options for Ruby in Eclipse


Rename

Rename


Move

Move


Change Method Signature

Merge Class Parts in File


Extract Local Variable

Pull Up


Extract Constant

Pull Down


Inline

Merge With External Class Parts


Convert Anonymous Class to Nested

Split Local Variable


Convert Member to Top Level

Merge With External Class Parts


Convert Local Variable to Field

Inline


Extract Super Class

Extract Constant


Extract Interface

Encapsulate Field


Extract Class

Convert Local Variable to Field


Use Supertype where possible


Pull Up


Pull Down


Introduce Parameter Object


Introduce Indirection


Introduce Factory


Introduce Parameter


Encapsulate Field


Generalize Declared Type


Infer Generic Type Arguments


Ease of Use and Integrated Develop Environment Integration
The refactoring options for Ruby and Java cover all the basic refactorings.  The differences in the number of options mainly come from the difference in the two languages. Ruby is a dynamically typed language, has unbounded polymorphism, and all classes are open to extension.  On the other hand, Java is a statically typed language, polymorphism is mainly implemented via interfaces and inheritance, and classes cannot be extended at run-time.  The given examples (in section 1.3, 1.4) illustrate the ease of use of the refactoring tools for both Ruby and Java and how well these tools are integrated into the Eclipse IDE.

References
[1] Thomas Corbat, Lukas Felber, Mirko Stocker Refactoring Support for the Eclipse Ruby Development Tools, Diploma Thesis, HSR University of Applied Sciences Rapperswil Institute for Software.

[2] Code Refactoring Wiki, http://en.wikipedia.org/wiki/Code_refactoring.

[3] The First Workshop on Refactoring, https://netfiles.uiuc.edu/dig/RefactoringWorkshop

[4] Refactoring Tutorial for Ruby on Rails, http://www.good-tutorials.com/tutorials/ruby-on-rails/refactoring

[5] Martin Fowler Refactoring: Improving the Design of Existing Code