- Change internal structure without changing external behavior
- TDD required - Test Suite
Benefits
- Enhance software design
- Improve readability
- Easier to find bugs
- Facilitate dev process
When to Refactor
- Rules of three: similar code repeated three times
- Preparatory refactoring: do before adding new feature
- Comprehension refactoring: do while reading a code
- Litter-pickup refactoring: do later
When NOT to Refactor
- External API / Blackbox
- When better to rewrite rather than refactor
Refactoring Approaches
- Basic Methods
- Extract / Inline method / variable
- Split phase (of a method)
- Encapsulation
- Extract class
- Encapsulate variable / collection
- Replace primitive with object
- Replace parameter with query
- Combine related functions into class
- Moving features
- Move method / field
- Split loop
- Replace loop with pipeline (MapReduce)
- Organizing Data
- Introduce parameter object
- Split variable
- Replace derived variable with query
- Change reference to value
- Simplifying Condition
- Decompose / Consolidate Condition
- Use Guard Clause for Nested Condition
- Replace condition with polymorphism
- Dealing with Inheritance
- Pull Up/Push Down Field/Method
- Extract Superclass
- Collapse Hierarchy (Remove subclass that does nothing additional)
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