CSC/ECE 517 Fall 2009/wiki 1a SJ

What is Code Refactoring

According to the famous book "Refactoring: Improving the Design of Existing Code " by Martin Fowler: 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

Java Example of Refactoring

Before rename:

public class rename_method
{
   static void badRenameMethod()
   {
       System.out.println("Hello, world!");
   }
}

After rename:

public class rename_method
{
   static void hello()
   {
       System.out.println("Hello, world!");
   }
}

Before encapsulation:

public class encap_field
{
   public String field;
}

After encapsulation:

public class encap_field
{
   private int field;

   public void setField(int field)
   {
       this.field = field;
   }

   public int getField()
   {
       return field;
   }
}

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 show 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 comparison:

1. Refactoring Options for Java in Eclipse		2. Refactoring Options in Eclipse for Ruby
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

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 runtime. 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 on ruby on rail, http://www.good-tutorials.com/tutorials/ruby-on-rails/refactoring