7.2 GRASP原则二：信息专家 Information Expert

2、GRASP原则二：信息专家 Information Expert
　　 What is a general principle of assigning responsibility to objects?

　　　　为一个对象 分配职责的一般原则是什么？

　　 “鸡鸣狗盗” 战国时候，齐国的孟尝君喜欢招纳各种人做门客，号称宾客三千….
2.2 GRASP rule2: Information Expert

　　 Name: Information Expert (信息专家)

　　 Problem:

　　　　 What is a general principle of assigning responsibility to objects?

　　 Solution:

　　　　 Assign responsibility to the class that has the information necessary to fulfill responsibility
　　 Information

　　　　 an object's own state,

　　　　 about other objects, the world around an object,

　　　　 information the object can derive,

　　　　 and so forth

　　 Answer to Mini exercise 2
2.3 Information Expert — How to?

　　 步骤

　　　　 1）Clearly state the responsibility

　　　　 2）Look in Design Model for relevant classes

　　　　 3）Else look in Domain Model and create design classes

　　 信息专家的优点

　　　　 封装性 Encapsulation

　　　　　　 对象充分利用自身的信息 objects support their own information

　　　　　　 支持低耦合 supports low coupling

　　　　 系统行为分布到不同的类 Behavior is distributed across classes

　　　　　　 支持高内聚 supports high cohesion