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As the application of object technology--particularly the Java programming language--has become commonplace, a new problem has emerged to confront the software development community. Significant numbers of poorly designed programs have been created by less-experienced developers, resulting in applications that are inefficient and hard to maintain and extend. Increasingly, software system professionals are discovering just how difficult it is to work with these inherited, "non-optimal" applications. For several years, expert-level object programmers have employed a growing collection of techniques to improve the structural integrity and performance of such existing software programs. Referred to as "refactoring," these practices have remained in the domain of experts because no attempt has been made to transcribe the lore into a form that all developers could use. . .until now. In Refactoring: Improving the Design of Existing Code, renowned object technology mentor Martin Fowler breaks new ground, demystifying these master practices and demonstrating how software practitioners can realize the significant benefits of this new process.
With proper training a skilled system designer can take a bad design and rework it into well-designed, robust code. In this book, Martin Fowler shows you where opportunities for refactoring typically can be found, and how to go about reworking a bad design into a good one. Each refactoring step is simple--seemingly too simple to be worth doing. Refactoring may involve moving a field from one class to another, or pulling some code out of a method to turn it into its own method, or even pushing some code up or down a hierarchy. While these individual steps may seem elementary, the cumulative effect of such small changes can radically improve the design. Refactoring is a proven way to prevent software decay.
In addition to discussing the various techniques of refactoring, the author provides a detailed catalog of more than seventy proven refactorings with helpful pointers that teach you when to apply them; step-by-step instructions for applying each refactoring; and an example illustrating how the refactoring works. The illustrative examples are written in Java, but the ideas are applicable to any object-oriented programming language.
1. Refactoring, a First Example.
The Starting Point.
The First Step in Refactoring.
Decomposing and Redistributing the Statement Method.
Replacing the Conditional Logic on Price Code with Polymorphism.
Why Should You Refactor?
When Should You Refactor?
What Do I Tell My Manager?
Problems with Refactoring.
Refactoring and Design.
Refactoring and Performance.
Where Did Refactoring Come From?
Long Parameter List.
Parallel Inheritance Hierarchies.
Alternative Classes with Different Interfaces.
Incomplete Library Class.
The Value of Self-testing Code.
The JUnit Testing Framework.
Adding More Tests.
Format of the Refactorings.
How Mature Are These Refactorings?
Replace Temp with Query.
Introduce Explaining Variable.
Split Temporary Variable.
Remove Assignments to Parameters.
Replace Method with Method Object.
Remove Middle Man.
Introduce Foreign Method.
Introduce Local Extension.
Self Encapsulate Field.
Replace Data Value with Object.
Change Value to Reference.
Change Reference to Value.
Replace Array with Object.
Duplicate Observed Data.
Change Unidirectional Association to Bidirectional.
Change Bidirectional Association to Unidirectional.
Replace Magic Number with Symbolic Constant.
Replace Record with Data Class.
Replace Type Code with Class.
Replace Type Code with Subclasses.
Replace Type Code with State/Strategy.
Replace Subclass with Fields.
Consolidate Conditional Expression.
Consolidate Duplicate Conditional Fragments.
Remove Control Flag.
Replace Nested Conditional with Guard Clauses.
Replace Conditional with Polymorphism.
Introduce Null Object.
Separate Query from Modifier.
Replace Parameter with Explicit Methods.
Preserve Whole Object.
Replace Parameter with Method.
Introduce Parameter Object.
Remove Setting Method.
Replace Constructor with Factory Method.
Replace Error Code with Exception.
Replace Exception with Test.
Pull Up Field.
Pull Up Method.
Pull Up Constructor Body.
Push Down Method.
Push Down Field.
Form Template Method.
Replace Inheritance with Delegation.
Replace Delegation with Inheritance.
Tease Apart Inheritance.
Convert Procedural Design to Objects.
Separate Domain from Presentation.
A Reality Check.
Why Are Developers Reluctant to Refactor Their Programs?
A Reality Check (Revisited).
Resources and References for Refactoring.
Implications Regarding Software Reuse and Technology Transfer.
A Final Note.
Refactoring with a Tool.
Technical Criteria for a Refactoring Tool.
Practical Criteria for a Refactoring Tool.