Refactoring & Code Smells

Definition of Refactoring

• Process of altering source code while preserving its functionality.

• Purpose: Improve maintainability, especially enhancement.

Key Aspects of Refactoring

• What Refactoring Is:

  • Small, safe, incremental changes.

  • Improves code design to be more understandable and flexible.

  • Breaking large methods into smaller ones.

  • Renaming variables and parameters meaningfully.

  • Moving responsibilities to appropriate classes.

  • Creating interfaces for classes.

• What Refactoring Is Not:

  • An excuse to make unrelated enhancements.

  • Merely adding features or improving error handling.

  • Filling gaps without clear need.

Importance of Refactoring

• Prevents design decay and code messiness.

• Simplifies code, increases readability and maintainability.

• Helps find bugs and reduces debugging time.

• Indicates a learning process about the application.

Design Decay

• Occurs in software systems where there is an absence of an upfront design.

• It describes a condition where code may be functionally correct and satisfying customers today but where the underlying implementation has become inefficient from a maintenance and evolution perspective.

When to Refactor

• When you add functionality

• When you learn something about the code

• When you fix a bug

• When the code smells

When not to Refactor

• When tests aren’t passing

• When you should just rewrite the code

• When you have impending deadlines

Problems with Refactoring

• Over-refactoring can lead to endless tinkering.

• Refactoring code when the tests don’t work leads to potentially dangerous situations.

• Databases can be difficult to refactor.

• Refactoring published interfaces can cause problems for the code that uses those interfaces.

Reasons For Reluctance To Refactor

• Lack of understanding

• Short-term focus

• Not paid for overhead task like refactoring

• Fear of breaking current program

Types of Refactoring (Fowler's List)

• Add Parameter

• Change Association Direction

• Extract Method

• Extract Class

• Rename Method

• Replace Magic Number with Constant

Code Smells

• Definition: A hint that something may be wrong in the code.

• Categories include:

  • Comments (indicating unclear code)

  • Duplicated Code

  • Long Methods

  • For Testers Only (methods solely for testing)

How to Identify Code Smells

• Experience

• Regular code review

• Tools that generate metrics. e.g. cyclomatic complexity

Cyclomatic Complexity

• Definition: Metric that measures the structural complexity of a method (decision points).

• Formula: $CC = ext{number of decision points} + 1$

• Impact: Higher complexity means more tests required, complicating maintenance.

Tool Support

• Tools to identify bad smells and control metrics in a software

• Examples include PMD, FindBugs, and JDeodorant among others.