| Principles
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Loose Coupling •
High Cohesion •
Change is Local •
It is Easy to Remove
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| Smells
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Rigidity •
Fragility •
Immobility •
Viscosity of Design •
Viscosity of Environment •
Needless Complexity •
Needless Repetition •
Opacity
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| Class Design
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| Package Cohesion
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Release Reuse Equivalency Principle (RREP) •
Common Closure Principle (CCP) •
Common Reuse Principle (CRP)
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| Package Coupling
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Acyclic Dependencies Principle (ADP) •
Stable Dependencies Principle (SDP) •
Stable Abstractions Principle (SAP)
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| General
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Follow Standard Conventions •
Keep it Simple, Stupid (KISS) •
Boy Scout Rule •
Root Cause Analysis
Multiple Languages in One Source File
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| Environment
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Project Build Requires Only One Step •
Executing Tests Requires Only One Step •
Source Control System •
Continuous Integration
Overridden Safeties
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| Dependency Injection
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Decouple Construction from Runtime
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| Design
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Keep Configurable Data at High Levels •
Don’t Be Arbitrary • Be Precise •
Structure over Convention •
Prefer Polymorphism To If/Else or Switch/Case •
Symmetry / Analogy •
Separate Multi-Threading Code
Misplaced Responsibility •
Code at Wrong Level of Abstraction •
Fields Not Defining State •
Over Configurability •
Micro Layers
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| Dependencies
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Make Logical Dependencies Physical
Singletons / Service Locator •
Base Classes Depending On Their Derivatives •
Too Much Information •
Feature Envy •
Artificial Coupling •
Hidden Temporal Coupling •
Transitive Navigation
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| Naming
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Choose Descriptive / Unambiguous Names •
Choose Names at Appropriate Level of Abstraction •
Name Interfaces After Functionality They Abstract •
Name Classes After How They Implement Their Interfaces •
Name Methods After What They Do •
Use Long Names for Long Scopes •
Names Describe Side Effects •
Standard Nomenclature Where Possible
Encodings in Names
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| Understandability
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Consistency •
Use Explanatory Variables •
Encapsulate Boundary Conditions •
Prefer Dedicated Value Objects to Primitive Types
Poorly Written Comment •
Obscured Intent •
Obvious Behaviour Is Unimplemented •
Hidden Logical Dependency
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| Methods
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Methods Should Do One Thing •
Methods Should Descend 1 Level of Abstraction
Method with Too Many Arguments •
Method with Out/Ref Arguments •
Selector/Flag Arguments •
Inappropriate Static
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| Source Code Structure
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Vertical Separation •
Nesting •
Structure Code into Namespaces by Feature
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| Conditionals
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Encapsulate Conditionals •
Positive Conditionals
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| Useless Stuff
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Dead Comment, Code •
Clutter •
Inappropriate Information
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| Maintainability Killers
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Duplication •
Magic Numbers / Strings •
Enums (Persistent or Defining Behaviour)
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| Exception Handling
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Catch Specific Exceptions •
Catch Where You Can React in a Meaningful Way •
Use Exceptions instead of Return Codes or null •
Fail Fast
Using Exceptions for Control Flow •
Swallowing Exceptions
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| From Legacy Code to Clean Code
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Always have a Running System •
1) Identify Features •
2) Introduce Boundary Interfaces for Testability •
3) Write Feature Acceptance Tests •
4) Identify Components •
5) Refactor Interfaces between Components •
6) Write Component Acceptance Tests •
7) Decide for Each Component: Refactor, Reengineer, Keep •
8a) Refactor Component •
8b) Reengineer Component •
8c) Keep Component
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| Refactoring Patterns
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Reconcile Differences – Unify Similar Code •
Isolate Change •
Migrate Data •
Temporary Parallel Implementation •
Demilitarized Zone for Components
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