CSC/ECE 517 Fall 2009/wiki1a 8 nd

Problem Statement

The list of refactorings has become quite long & people don't remember long lists very well. To promote learning the different patterns, they should be categorized in some way, or perhaps, along various dimensions. Here is an attempt to categorize the various available refactoring methods into different categories along as many different dimensions as makes sense. As a reference we have taken the list of refactorings methods available at http://www.refactoring.com/catalog/index.html.

Categorization of Refactoring Methods

Categorization Framework Used

When an application is developed using an object oriented programming language the code architecture is designed in the following way. First the functionality of the application is divided into major chunks & assigned to sets of packages which form the first level of hierarchy for the program.

The second level of hierarchy are the compilation units which has access to all types declared in its package and also automatically import all of the public types(in other packages/files) declared in the package. Types consist of classes & interfaces.

The functionality implemented in a package is further broken down & implemented using classes at the third level of hierarchy. Classes are made out of items, which are basically methods & fields. Fields declare data which are associated with the class. Interfaces encode the similarities among classes.

In order to store multiple values of the same type of data, the fourth level of hierarchy i.e. a # of objects are created which act as data structures and store data associated with the class.

At the lowest level i.e the fifth is the data, which is a part of the object & also at this level is the code which processes this data, which is a part of the method.

This hierarchy is followed during any application development using an object oriented language & when an analyst is asked to refactor code, he/she also parses through this same hierarchy to understand the code functionality & to find spots where the code can be refactored.

Most of the refactoring methods belong to level 3, level 4 and level 5, hence these categories have again been divided into sub-categories, to reduce generalization & make the categorization more specific. Here is an attempt to make categorization of the refactoring methods based on the said hierarchy. Also there are a two categories whose inspiration isn't the above hierarchy.Here are the categories & sub-categories using which the refactorings methods available at http://www.refactoring.com/catalog/index.html have been categorized.

Categories

Refactoring the Package

A refactoring method will fall under this category if the changes made affect the package structure or add to the functionality to the package. The refactoring method generally may involve breaking the functionality of a package to smaller packages or moving classes to a more relevant package.

*Extract Package
*Move Class

Refactoring the Class

• Changing Class Association

A refactoring method falls in this category if it tries to change the association between two classes so that features to a class may be added or removed.

**Change Unidirectional Association to Bidirectional
**Change Unidirectional Association to Bidirectional

• Change of Class Structure

A refactoring method falls in this category when it tries to change the hierarchy, classes share amongst them.

**Collapse Hierarchy
**Duplicate Observed Data
**Extract Class
**Extract SubClass
**Extract SuperClass
**Inline Class
**Replace Subclass with Fields
**Separate Data Access Code

• Addition to a Class *What about the ulta of this?

A refactoring method falls in this category when it tries to add functionality to a class. This may involve adding constructors, feilds or methods to a class.

**Pull up Constructor Body
**Pull up Field
**Pull up Method
**Push Down Field 
**Push Down Method

Refactoring the Method

• Meaningful and Detailed Method Calls

A refactoring method will fall under this category if it modifies a method call to pass more data to the method or tries to make the method call more understandable.

**Add Parameter
**Preserve Whole Object
**Rename Method

• Change of Structure of the Method Code

A refactoring method will fall under this category if it deliberately changes the internal flow of the code without affecting the output. These methods need not result in the optimization of the code or simplification.

**Consolidate Conditional Expression
**Encapsulation Collection
**Extract Method
**Inline Method
**Form Template Method
**Replace Nested Conditional with Guard Clauses
**Replace Parameter with Method

• Change Method Call Hierarchy/Sequence

A refactoring method will fall in this category when it tries to change the method call flow in any way.

**Remove Middle man
**Replace Delegation with Inheritance
**Replace Inheritance with Delegation

• Improve Method Readability

A refactoring method will fall under this category when it increases the readability of the code for a new person reading the code or for debugging purpose if ever needed.

**Introduce Explaining Variable
**Replace Magic No with Symbolic Constant 
**Split Temporary Variable

• Method Code Refactoring based on Method Arguments

A refactoring method will fall under this category when it makes the behavior of the executed method code, change depending on the argument passed, or when it frees the method code of this feature.

**Replace Conditional with Polymorphism
**Replace Conditional with Visitor
**Replace Parameter with Explicit Methods

Refactoring the Object

• Replacements with Objects

A refactory method will fall under this category when the code is changed such that its execution is more centered around the object. And different parameters like array, data values are replaced by objects.

**Introduce Null Object
**Introduce Parameter Object
**Replace Array with Object
**Replace Data Value with Object
**Replace Method with Method Object

• Object Initialization

**Replace Constructor with Factory Method

• Accessing the Object/Data

A refactory method will fall under this category Accessing the object / Data if the method changes the way an object or data is accessed.

**Change Reference to Value
**Change Value to Reference
**Refactor Architecture by Tiers
**Self Encapsulate Field

Refactoring the Code

• Code Optimization

A refactoring method will fall under this category when the method brings about change in the code such a way that its execution is optimized.

**Consolidate Duplicate Conditional Fragments
**Decompose Conditional
**Inline Temp
**Introduce Assertion
**Remove Control Flag
**Replace Iteration with Recursion
**Replace Temp with Query

• Redundant Code Elimination

A refactoring method will fall under this category if it helps to eliminate the unnecessary code and makes the code cleaner.

**Parametrize Method
**Remove Parameter

• Method Code Simplification

A refactoring method will fall under this category when it causes simplification of the code making it more readable & understandable, it may or may not optimize the execution.

**Encapsulate Downcast
**Reduce Scope of Variable
**Remove Double Negative
**Replace Assignment with Initialization
**Reverse Conditional
**Separate Query from Modifier
**Split Loop
**Substitute Algorithm

• Removal of "Type Code"

A refactory method will fall under the category Removal of "Type Code" if the method helps to remove the type code.

**Replace Type Code with Class
**Replace Type Code with State/Strategy
**Replace Type Code with Subclasses

Refactoring for Privacy

A refactoring method will fall under this category if it helps in data protection and privacy.

*Encapsulate Field
*Hide Delegate
*Hide Method
*Hide Presentation Tier-Specific Details from the Business tier
*Introduce Business Delegate
*Wrap Entities with Session

Dealing with Exceptions

*Remove Error Code with Exception
*Replace Exception with Test

References

http://www.refactoring.com
Refactoring: Improving the Design of Existing Code by Martin Fowler.