In this section, I present a catalog of refactorings, many of which I describe by summarizing the more detailed descriptions presented in Refactoring (Fowler 1999). I have not, however, attempted to make this catalog exhaustive. In a sense, every case in this book that shows a "bad code" example and a "good code" example is a candidate for becoming a refactoring. In the interest of space, I've focused on the refactorings I personally have found most useful.
Here are refactorings that improve the use of variables and other kinds of data.
Replace a magic number with a named constant. If you're using a numeric or string literal like 3.14, replace that literal with a named constant like PI.
Rename a variable ...