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 main refactoring

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

Some Ruby Example of refactoring

before rename:

def badRenameMethod
   puts("Hello World");
end

after rename:

def hello
put("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

Some 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

example of rename:

example of encapsulation:

Example of using Java refactoring tools in Eclipse

example of rename:

example of encapsulation:

Comparison of Ruby and Java refactoring tools

Comprehensiveness:

Convert Local Variable to Field

Encapsulate Field

Extract Constant

Inline

Merge Class Parts in File

Merge With External Class Parts

Move

Pull Up

Pull Down

Rename

Split Local Variable

Rename

Move

Change Method Signature

Extract Local Variable

Extract Constant

Inline

Convert Anonymous Class to Nested

Convert Member to Top Level

Convert Local Variable to Field

Extract Super Class

Extract Interface

Extract Class

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 dynamically typed language, has unbounded polymorphism, and all classes are open to extension. On the other hand, Java is statically typed, polymorphism is mainly implemented via interfaces and inheritance, and classes cannot be extended at runtime. The given examples 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