1.Duplicated Code     Same expression in two methods of the same class: Extract Method     Same expression in two sibling subclass:Extract Method ,then Pull Up Field     Duplicated code in two unrelated classs:Extract Class/The method belongs only in one class and be invoked by the other class.
  2.Long Method    A heuristic we follow is that whenever we feel the needd to comment something,we write a method instead(Extract Method).A good technology to identify the clumps of code to extract is to look for comments.Conditionals and loops also give signs for extraction. 3.Large Class    Extract Method 4.Long Parameters List    Replace Parameter with Method, Preserve Whole Object, Introduce Parameter Object. 5.Divergent Change    Extract Class. 6.Shotgun Surgery    Move Method, Move Field, Inline Class,. 7.Feature Envy    Move Method, Extract Method,. 8.Data Clumps    Extract Class, Introduce Parameter Object, Preserve Whole Object 9 Primitive Obseesion 10.Switch Statements     Extract Method 11.Parallel Inheritance Hierarchis 12.Lazy Class  13.Speculative Generality 14.Temporary Field 15.Message Chains 16.Middle Man 17.Inappropriate Intimacy 18.Alternative Classes with Different Interfaces 19.Incomplete Library Class 20.Data Class  21.Refused Bequest    Push Down Method and Push Down Field 22.Comments  
 
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