Is changing the interface of part of the code a refactoring?

Is it a refactoring to change the order of declarations, eg methods and fields in a Java program?

Here's an interesting conundrum posed by Przemyslaw Pokrywka. One of the refactorings in the book is Introduce Null Object - a very useful refactoring (also discussed in Josh's new book.) Przemyslaw's point is that this refactoring can alter behavior. If you have a method return a null, and you invoke a method on that null you'll get a null pointer exception. If you use a Null Object you'll get some default behavior.

If you make a change to improve the performance of a program, is this a refactoring?

There was some recent discussion on the refactoring mailing list about what is or isn't a refactoring. As with these discussions, there's always a danger of debating how many angels fit on a pin, but thinking about the boundaries does have some useful purpose.