What is the effect of refactoring on external behavior?

• A. Refactoring should always change external behavior.
• B. Refactoring should improve structure while keeping external behavior the same.
• C. External behavior should be rewritten to reflect new features.
• D. Refactoring is only about renaming variables.

Answer: (B)

Refactoring focuses on preserving what the program does for users while improving how the code is organized. External behavior is the observable result of running the program—the inputs it accepts, the outputs it produces, and the side effects users can see. The goal of refactoring is to clean up the internal structure, make the code easier to read, test, and maintain, and perhaps make future changes easier, all without altering those observable interactions. That’s why the best choice says it should improve structure while keeping external behavior the same. If you change external behavior while refactoring, you’ve left the realm of cleanup and moved into implementing new features or altering requirements.

To illustrate, you might extract a long function into smaller ones, rename internal variables for clarity, or reorganize modules—changes that make the code clearer and safer to modify without changing what the program does from the outside. The other statements miss the core idea: refactoring isn’t about rewriting how the system behaves or about only renaming things; it’s about internal improvement while keeping behavior intact.