CSC/ECE 517 Fall 2011/ch5 5d he

Automatic Refactoring

Introduction

Refactoring is a technique for restructuring an existing code, altering its internal structure without changing its external behavior. Its done as a series of small transformations. Each transformation does little, but a sequence of transformations can produce a significant restructuring. Since each refactoring is small, it's less likely to go wrong. The system is also kept fully working after each small refactoring, reducing the chances that a system can get seriously broken during the restructuring.<ref name="refone"> Refactoring Home Page http://refactoring.com/ </ref> As people make changes to the code to realize their short term goals without fully understanding the design of code, the code loses its structure. The refactoring work is done to remove bits that aren’t really in the right place. Loss of the structure of code has a cumulative effect. The harder it is to see the design in the code, the harder it is to preserve it, and the more rapidly it decays. Regular refactoring helps code retain its shape. <ref name="reftwo"> Why should you Refactor http://sourcemaking.com/refactoring/why-should-you-refactor </ref>

Fully autonomous factoring doesn't appear to exist at this time in the IDE(s) described below. However there are papers Inducing Evolution-Robust Pointcuts <Ref name="refseven">Inducing Evolution-Robust Pointcuts, Braem, M.</ref> and Automatic Refactoring of Erlang Programs<ref name="refeight">Automatic Refactoring of Erlang Programs http://www.ece.cmu.edu/~aavgerin/papers/PPDP09.pdf</ref> that point the way to the future of refactoring that can be fully automated. In the context of this wiki article, automatic refactoring means automated refactoring under programmer control and guidance.

Common Refactoring Techniques

Extraction Refactoring

There are several refactoring techniques related to extraction: Extract method, Extract local variables, extract constants. The first method "Extract method will create a new method from code you've selected. Extract Local Variable refactoring takes an expression that is being used repeatedly and assigns it to a local variable. Extract constant refactoring is to select a static, constant expression, which the refactoring will convert to a static final constant. This is useful for removing hard-coded numbers and strings from your code

Inline Refactoring

This type refactoring is the reverse of local variable extraction, in which we remove a local variable and use the value of the variable(typically an expression) in the place where the variable is used. This can be marginally more efficient than using a temporary variable and, by making the code terser, makes it either easier to read or more cryptic, depending on your point of view<ref name="refthree"> refactoring for everyone http://www.ibm.com/developerworks/library/os-ecref/ </ref>

Encapsulating Fields

Generally its not a good practice to expose the class attributes through public interface. Thus, Encapsulating such fields will make such fields as private or protected as appropriate and generate getters and setters for the associated field.

Changing Method Signature

Here we change the change the parameters, visibility, and return type of a method.

Other Refactorings

There are a multitude of refactorings. Those that are included with RubyMine<ref name="reffour">RubyMine :: Ruby and Ruby on Rails IDE with smart code completion, syntax highlighting and refactoring http://www.jetbrains.com/ruby/features/ruby_ide.html#Refactorings</ref> include:

• Rename refactoring
• Extract Method
• Extract Module
• Extract Superclass
• Introduce Variable
• Introduce Constant
• Introduce Field
• Introduce Parameter
• Inline Variable
• Pull Uo Members
• Push Down Members
• Override Method

Martin Fowler has online resources for additional refactoring definitions which can be found here http://martinfowler.com/bliki/refactoring.html<ref name="reffive">MF Blicki: refactoring http://martinfowler.com/bliki/refactoring.html</ref> and here http://refactoring.com/catalog/<ref name="refsix">Alpha list of refactorings http://refactoring.com/catalog/</ref>.

Refactoring support in popular IDE(s)

IDE	Refactoring Support	Automated Refactoring?	Number of Refactoring support	Support for Pattern	Example
Borland Delphi
Eclipse <ref name='refeclipse'>Eclipse Refactoring Actions http://help.eclipse.org/indigo/index.jsp?topic=%2Forg.eclipse.jdt.doc.user%2Freference%2Fref-menu-refactor.htm </ref>	Rename selected Elements, Move selected elements, Change Method Signature, Extraction, Convert Anonymous Class to Nested, Convert Local Variable to Field, Extract Super class and Interface, push down, pull up, Introduce Indirection, Encapsulate Field, Migrate JAR File, Create & Apply Refatoring Scripts		Yes	Introduce Factory,	int x= p * 5; > int x= getFoo(p); (Method Extraction) , p.x; > p.getX() (Encapsulate Field)
Kdevelop
NetBeans
Padre
RubyMine	No	Yes	11
Visual Studio	Extract Method, Encapsulate Field, Extract Interface, Rename, Promote Variable to Parameter(Changing method signature), Generate Method Stub(Used for testing purposes)			Promoting Variable to Parameter Before Refactoring public void MethodA() { MethodB(); } public void MethodB() { string output = "Test String"; MessageBox.Show( output); } After Refactoring public void MethodA() { MethodB("Test String"); } public void MethodB(string output) { MessageBox.Show( output); }

References

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