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Code refactoring is the process of restructuring existing computer code – changing the ''factoring'' – without changing its external behavior. Refactoring improves ''nonfunctional'' attributes of the software. Advantages include improved code readability and reduced complexity; these can improve source code maintainability and create a more expressive internal architecture or object model to improve extensibility. Typically, refactoring applies a series of standardised basic ''micro-refactorings'', each of which is (usually) a tiny change in a computer program's source code that either preserves the behaviour of the software, or at least does not modify its conformance to functional requirements. Many development environments provide automated support for performing the mechanical aspects of these basic refactorings. If done extremely well, code refactoring may also resolve hidden, dormant, or undiscovered computer bugs or vulnerabilities in the system by simplifying the underlying logic and eliminating unnecessary levels of complexity. If done poorly it may fail the requirement that external functionality not be changed, and/or introduce new bugs. ==Overview== Refactoring is usually motivated by noticing a code smell. For example the method at hand may be very long, or it may be a near duplicate of another nearby method. Once recognized, such problems can be addressed by ''refactoring'' the source code, or transforming it into a new form that behaves the same as before but that no longer "smells". For a long routine, one or more smaller subroutines can be extracted; or for duplicate routines, the duplication can be removed and replaced with one shared function. Failure to perform refactoring can result in accumulating technical debt; on the other hand, refactoring is one of the primary means of repaying technical debt. There are two general categories of benefits to the activity of refactoring. # Maintainability. It is easier to fix bugs because the source code is easy to read and the intent of its author is easy to grasp. This might be achieved by reducing large monolithic routines into a set of individually concise, well-named, single-purpose methods. It might be achieved by moving a method to a more appropriate class, or by removing misleading comments. # Extensibility. It is easier to extend the capabilities of the application if it uses recognizable design patterns, and it provides some flexibility where none before may have existed.〔 Before refactoring a section of code, a solid set of automatic unit tests is needed. The tests are used to demonstrate that the behavior of the module is correct before the refactoring. If it inadvertently turns out that a test fails, then it's generally best to fix the test first, because otherwise it is hard to distinguish between failures introduced by refactoring and failures that were already there. After the refactoring, the tests are run again to verify the refactoring didn't break the tests. Of course, the tests can never prove that there are no bugs, but the important point is that this process can be cost-effective: good unit tests can catch enough errors to make them worthwhile and to make refactoring safe enough. The process is then an iterative cycle of making a small program transformation, testing it to ensure correctness, and making another small transformation. If at any point a test fails, the last small change is undone and repeated in a different way. Through many small steps the program moves from where it was to where you want it to be. For this very iterative process to be practical, the tests must run very quickly, or the programmer would have to spend a large fraction of his or her time waiting for the tests to finish. Proponents of extreme programming and other agile software development describe this activity as an integral part of the software development cycle. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Code refactoring」の詳細全文を読む スポンサード リンク
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