Refactoring 

What is refactoring? 

"A change to the system that leaves its behavior unchanged, but enhances some nonfunctional quality – simplicity, flexibility, understandability, performance" Kent Beck, Extreme Programming Explained 

"A change made to the internal structure of software to make it easier to understand and cheaper to modify without changing its observable behavior" Martin Fowler, Refactoring 

Why refactoring? 

Prevent “design decay” Clean up messes in the code Simplify the code 

Increase readability and understandability Find bugs Reduce debugging time 

How to refactor? 

1. Make sure your tests pass 2. Find some code that “smells” 3. Determine how to simplify this code 4. Make the simplifications 5. Run tests to ensure things still work correctly 6. Repeat the simplify/test cycle until the smell is gone 

When to refactor? 

When you add functionality When you learn something about the code When you fix a bug When the code smells 

“Here’s a guideline Don Roberts gave me: The first time you do something, you just do it. The second time you do something similar, you wince at the duplication, but you do the duplicate thing anyway. The third time you do something similar, you refactor.” The Three Rule, Marting Fowler 

When NOT to refactor? 

When the tests aren’t passing When you should just rewrite the code When you have impending deadlines 

“The other time you should avoid refactoring is when you are close to a deadline. At that point the productivity gain from refactoring would appear after the deadline and thus be too late” Marting Fowler 

Code Smells 

Indicators that something may be wrong in the code Can occur both in production code and test code 

The Bloaters -Long Method -Large Class -Primitive Obsession -Long Parameter List -DataClumps 

The Object-Orientation Abusers -Switch Statements -Temporary Field -Refused Bequest -Alternative Classes with Different Interfaces 

The Change Preventers -Divergent Change -Shotgun Surgery -Parallel Inheritance Hierarchies 

The Dispensables -Lazy class -Data class -Duplicate Code -Dead Code, -Speculative Generality 

The Couplers -Feature Envy -Inappropriate Intimacy -Message Chains -Middle Man 

Refactors