上海交通大学：《面向对象分析与设计 Object Oriented Analysis and Design》课程教学资源（PPT课件讲稿）15 Class Design

Shanghai Jiao Tong University 上海交通大学 Object Oriented Analysis and Design Class Design 上海交通大学软件工程中心

Shanghai Jiao Tong University 上海交通大学软件工程中心 Object Oriented Analysis and Design Class Design

Class Design in Context [Early Elaboration [Inception Iteration] Iteration (Optional)] Define a Candidate Perform Architecture Architectural L Synthesis Analyze Behavior (Optional) Refine the Architecture Class Design Designer Define Design the Components Database Object Oriented Analysis and Design 2

Object Oriented Analysis and Design 2 Class Design in Context [Early Elaboration Iteration] [Inception Iteration (Optional)] Define a Candidate Architecture Perform Architectural Synthesis Analyze Behavior Refine the Architecture Define Components Design the Database (Optional) Class Design Designer

Class Design Overview Project Specific Guidelines Class Design Design Classes Supplementary Specifications Object Oriented Analysis and Design 3

Object Oriented Analysis and Design 3 Class Design Overview Supplementary Specifications Class Design Project Specific Guidelines Design Classes

Outline Create Initial Design Classes ◆Define Operations ◆Define Methods ◆Define States ◆Define Attributes ◆Define Dependencies ◆Define Associations ◆ Define Generalizations Object Oriented Analysis and Design 4

Object Oriented Analysis and Design 4 Outline  Create Initial Design Classes  Define Operations  Define Methods  Define States  Define Attributes  Define Dependencies  Define Associations  Define Generalizations

Outline Create Initial Design Classes ◆Define Operations ◆Define Methods ◆Define States ◆Define Attributes ◆Define Dependencies ◆Define Associations Define Generalizations ◆ Object Oriented Analysis and Design 5

Object Oriented Analysis and Design 5 Outline  Create Initial Design Classes  Define Operations  Define Methods  Define States  Define Attributes  Define Dependencies  Define Associations  Define Generalizations

Class Design Considerations Class stereotype Boundary Entity Control Applicable design patterns Architectural mechanisms Persistence Distribution etc. Object Oriented Analysis and Design 6

Object Oriented Analysis and Design 6 Class Design Considerations  Class stereotype ▪ Boundary ▪ Entity ▪ Control  Applicable design patterns  Architectural mechanisms ▪ Persistence ▪ Distribution ▪ etc

How Many Classes Are Needed? Many,simple classes means that each class Encapsulates less of the overall system intelligence Is more reusable Is easier to implement A few,complex classes means that each class ■ Encapsulates a large portion of the overall system intelligence Is less likely to be reusable Is more difficult to implement A class should have a single well-focused purpose.A class should do one thing and do it well! Object Oriented Analysis and Design 7

Object Oriented Analysis and Design 7 A class should have a single well-focused purpose. A class should do one thing and do it well! How Many Classes Are Needed?  Many, simple classes means that each class ▪ Encapsulates less of the overall system intelligence ▪ Is more reusable ▪ Is easier to implement  A few, complex classes means that each class ▪ Encapsulates a large portion of the overall system intelligence ▪ Is less likely to be reusable ▪ Is more difficult to implement

Strategies for Designing Boundary Classes User interface (Ul)boundary classes ■ What user interface development tools will be used? How much of the interface can be created by the development tool? ◆ External system interface boundary classes Usually model as subsystem MainWindow SubWindow MainForm Button DropDownList Object Oriented Analysis and Design 8

Object Oriented Analysis and Design 8 Strategies for Designing Boundary Classes  User interface (UI) boundary classes ▪ What user interface development tools will be used? ▪ How much of the interface can be created by the development tool?  External system interface boundary classes ▪ Usually model as subsystem MainForm SubWindow Button DropDownList MainWindow

Strategies for Designing Entity Classes ◆ Entity objects are often passive and persistent Performance requirements may force some re-factoring ◆ See the Identify Persistent Classes step Analysis Design FatClass FatClass -privateAttr privateAttr -commonlyUsedAttr1 getCommonlyUsedAttr1() commonlyUsedAttr2 getCommonlyUsedAttr2() rarelyUsed1 getRarelyUsedAtt1() -rarelyUsed2 getRarelyUsedAtt2() 0.1 FatClassDataHelper FatClassLazy DataHelper commonlyUsedAttr1 -rarelyUsedAttr1 commonlyUsedAttr2 rarelyUsedAttr2 Object Oriented Analysis and Design 9

Object Oriented Analysis and Design 9 Strategies for Designing Entity Classes  Entity objects are often passive and persistent  Performance requirements may force some re-factoring  See the Identify Persistent Classes step Analysis FatClassLazyDataHelper - rarelyUsedAttr1 - rarelyUsedAttr2 Design FatClass - privateAttr + getCommonlyUsedAttr1() + getCommonlyUsedAttr2() + getRarelyUsedAtt1() + getRarelyUsedAtt2() FatClassDataHelper - commonlyUsedAttr1 - commonlyUsedAttr2 1 0..1 FatClass - privateAttr - commonlyUsedAttr1 - commonlyUsedAttr2 - rarelyUsed1 - rarelyUsed2 >

Strategies for Designing Control Classes What happens to Control Classes? Are they really needed? Should they be split? ◆How do you decide? Complexity Change probability ■ Distribution and performance Transaction management Object Oriented Analysis and Design 10

Object Oriented Analysis and Design 10 Strategies for Designing Control Classes  What happens to Control Classes? ▪ Are they really needed? ▪ Should they be split?  How do you decide? ▪ Complexity ▪ Change probability ▪ Distribution and performance ▪ Transaction management