Brain Class is a class that is complex partly because it implements a significant amount of system intelligence and partly because it holds one or more Brain methods.


  • Low cohesion impacts understandability, maintainability and testability.
  • Since a Brain Class becomes less cohesive or non-cohesive, refactoring becomes painful. Moreover, refactoring of Brain methods which are large and complex becomes even more complicated.


  • The class is very large and complex (high LOC and has complex methods).
  • The class has either:
    • One Brain method and size of all methods is very large, Or,
    • Has more than one Brain Methods, and methods are large and functional complexity is very high.
  • The class is non-cohesive.
  • The class is not a God class because it does “not” access foreign data significantly.


Analysis of class TokenMaker indicates:

  • TokenMaker has 14 methods and 12 attributes.
  • A Brain Method: A represents public method markTokens( )
  • B Brain Method: B represents private method handleRule( )
  • C Brain Method: C represents private method markKeyword( )
  • Additionally: A, B, and C methods are represented as lengthy blocks indicating that their individual number of lines of code is significantly high.


  • Split a non cohesive class into two or more cohesive classes. Follow the ‘one class one task’ rule.
  • When creating class methods, avoid creating large and complex methods.
  • Try refactoring Brain methods by splitting them into multiple methods (refer to guidelines of ‘Brain Method’ on how to split Brain methods).
  • Brain methods tend to use significant duplicate code. Extract duplicate code into separate methods.
  • Brain methods are often a result of incremental additions of functionality to existing methods. When adding new code to an existing method, keep LOC within limit. If not, create a new method
  • In some cases a Brain class may be harmless, especially if proved over time that it has had no maintenance problems and is stable. In such a case avoid the costly effort of refactoring such a class.