Design Patterns笔记

一些笔记。

• strategy : facilitates the switch of the different but related algorithms/behaviors
• observer
• proxy : controls the access to the real subject ; shares the common interface with the real subject and sometimes provides a subset of the operations in the interface (in the case of the protection proxy)

     e.g. there are three kinds of proxies : (1) the remote proxy (surrogate the subject in the different address space); (2) the virtual proxy (SqlSessionTemplate in the mybatis.spring which is a proxy of the SqlSession); (3) the protection proxy (usually used in the os to control access to critical resouces)

• template method : constructs the skeleton of the algorithm and leaves the variant part to be implemented by the subclasses
• adapter : provides a uniform interface to the client which hides the different classes, usually inaccessible to clients

 

 

TO-DO: Open-Close Principle:

Conclusion

Like every principle OCP is only a principle. Making a flexible design involves additional time and effort spent for it and it introduce new level of abstraction increasing the complexity of the code. So this principle should be applied in those area which are most likely to be changed.

 

There are many design patterns that help us to extend code without changing it. For instance the Decorator pattern help us to follow Open Close principle. Also the Factory Method or the Observer pattern might be used to design an application easy to change with minimum changes in the existing code.