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
