面向对象方法下的模块化.pptxVIP

面向对象方法下的模块化Outline面向对象方法中的模块 – 类面向对象方法中的耦合访问耦合继承耦合类之间耦合的度量面向对象方法中的内聚模块化的不同表现结构化方法面向对象方法模块函数类接口函数的声明所有的public的成员变量和成员方法实现函数的定义所有的private的成员变量、成员方法、以及public方法的内部实现模块化的目标高内聚低耦合面向对象中的耦合交互耦合（同结构化）关联耦合继承耦合前提C和C’关联关联耦合类型耦合性解释例子Hidden最高C’既没在C的规格说明中出现，也没在实现中出现Cascading MessageScattered?C’还没有在C的规格说明中，但散落在实现中（局部变量或者成员变量）通过引入局部变量，避免Cascading MessageSpecified?C’在C的规格说明中类的规格说明中包含所有需接口和供接口（需要特殊语言机制）Nil最低理论最优，无关联耦合，维护时不需要对方任何信息完全独立HiddenC’ shows up neither in the specification nor in the implementation of CScatteredIf C’ is used as domain in the definition of some local variable or instance variable in the implementation of the definition of some local variable or instance variable in the implementation of C yet C’ is not include in the specification of CSpecified If C’ is included in the specification of C whenever it is a component of C降低关联耦合的方法针对接口编程接口分离原则（ISP）依赖倒置原则（DIP）迪米特法则针对接口编程Viewpoint：接口的规格原则：针对接口编程例子：Modula-3ISPViewpoint：接口最小化原则：接口分离Interface Segregation Principle (ISP)Many client specific interfaces are betterthan one general purpose interfaceClients should not be forced to dependupon interfaces they dont useISP ExplainedMultipurpose classesMethods fall in different groupsNot all users use all methodsCan lead to unwanted dependenciesClients using one aspect of a class also depend indirectly on the dependencies of the other aspectsISP helps to solve the problemUse several client-specific interfaces例子ISP SummaryWhen a class (Server) collects interfaces for various purposes (Clients) → fat interfaceUse separate interfaces to hide parts of the Server interface for ClientsSimilar to data hidingOr split the Server in several partsBe careful with vertical multiple inheritanceYou might drag in dependencies you dont want/need/like依赖倒置Viewpoint: 访问的方向性原则：依赖倒置Dependency Inversion Principle (DIP)Details should depend on abstractions.Abstractions should not depend on details.1) High level modules should not depend onlow level modules. Both should dependupon abstractions (interfaces