1. Class and Method Design
Chapter 14

2. Key Concepts
Low-level or detailed design is critical despite libraries and components
Pre-existing classes need to be understood and organized
Some, if not all code, is generally still needed to instantiate new classes

3. DESIGN CRITERIA

4. Coupling Interdependency among modules
Interaction coupling through message passing

5. Types of Interactive Coupling
Level Type
Good No Direct Coupling
Data
Stamp
Control
Common or Global
Bad Content or Pathological

6. Cohesion “Single-mindedness of a module” Method cohesion
Class cohesion
Generalization/specialization cohesion

7. Types of Method Cohesion
Level Type
Good Functional
Sequential
Communicational
Procedural
Temporal or Classical
Logical
Bad Coincidental

8. Types of Class Cohesion
Level Type
Good Ideal
Mixed-role
Mixed-domain
Worse Mixed-instance

9. Connascence
Creating the need to change another module as a result of changing one
Minimize overall connascence
Minimize across encapsulation boundaries
Maximize within encapsulation boundary

10. OBJECT DESIGN ACTIVITIES

11. Additional Specification
First review the current set of models
Sufficient but only necessary classes to solve problem
No missing attributes or methods
No extraneous attributes or methods
Examine visibility

12. Signatures for each method
Name of the method
Parameters or arguments to pass
Type of value the method will return to the calling method

13. Identify Opportunities for Reuse
Patterns
Framework
Class libraries
Components

14. Simple Contract Format
Method Name: Class Name: ID:
Clients (Consumers):
Associated Use Cases:
Description of Responsibilities:
Arguments Received:
Type of Value Returned:
Pre-Conditions:
Post-Conditions:

15. METHOD SPECIFICATION

16. Syntax No formal syntax specification General information Events
Message Passing
Algorithm Specification

17. Structured English

18. Pseudocode Example (Get CD-info module) Accept (CD_title) {Required}
Accept (CD_artist) {Required}
Accept (CD_category) {Required}
Accept (CD_length)
Return

19. Summary
Translating the basic elements of OO analysis into design requires attention to prevent difficulties and conflicts in execution.
Coupling, cohesion, and connascence are proposed for criteria for evaluating design.
The designer will look for opportunities to optimize the design, will create constraints and contracts, and will specify methods.