Refactoring Improving the Design of Existing Code

1. Bad smells in code

2. Duplicated code

• when same expression, Extract Method
• sibling in subclass,extract method and pulll up method in super class
• similar code ,but not identical,will extract Template method

3. Long Method

• long Method is difficult understand.
• small Method name will explain function.
• logic in loop  will extract method
• replace method with method object
• decompose conditional

4. Large Class

• many instance and duplicated code will happen in large class
• extarct subclass
• extarct interface group by function
• duplicate observed Data

5. Long Parameter List

• difficulte to understand paramter
• Preserve whole object

6. Divergent Change

7. Shotgun Surgery

• Move method and move field in one class

8. Feature Envy

9. Data Clumps

10. Primitive Obsession

• record type
• primitive types

11. Switch Statements

• cause by type code
• replace type code with subclasses
• replace type with state/strategy
• replace conditional with polymorphism
• replace parameter with Explicit methods

12. Parallel inheritance hieratchies

• same pre in other class is bad smell

13. Lazy Class

14. Speculative generality