1. SOEN 343 Software Design
Computer Science and Software Engineering Department
Concordia University
Fall 2005
Instructor: Patrice Chalin

2. Agenda – Lecture 11a GRASP interrelationships.
Dice Game Test class: a solution.
GoF
(Simple) Factory
Singleton
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SOEN 343, © P.Chalin,

3. GRASP Information Expert Creator High Cohesion Low Coupling Controller
Polymorphism
Pure Fabrication
Indirection
Protected Variations
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4. GRASP: Interrelationships
This is how Larman illustrates the interrelationships between the GRASP.
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5. Dice Game Test Class: A Solution
(Given in class)
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6. Gang Of Four Gamma, Helm, Johnson, Vlissides SOEN 343, © P.Chalin,
Erich
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7. GoF Pattern Summary (& Relationhips)
[Picutre (c) GoF CD]
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8. Design Issue: Ensure No More Than One Instance of a Class is Created
Given a class C, how can we ensure that only one instance of C is ever created?
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9. Converting C to a Singleton.
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10. Singleton Pattern Notice: Constructor is no longer public.
To access the instance use getUniqueInstance().
All other attribute and method declarations of C stay the same.
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11. «Singleton» C.getUniqueInstance()
public static C getUniqueInstance() {
if(uniqueInstance == null) {
uniqueInstance = new C(); }
return uniqueInstance;
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12. Thread-safe Creation Method
public static synchronized C getUn…() { … }
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13. Singleton: Design Alternatives/Issues
Create a class with static attributes and methods.
Trade-offs: consider how easy the following are:
Adapting the design so that x instances can be created (where x > 1).
Subclassing.
Passing the instance as a parameter. …
(See Larman05, Section 26.5)
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14. Singleton: Design Issues (Cont’d)
See Larman05, Section 26.5 for discussion of
Design trade-offs, including
eager/lazy evaluation of Singleton.uniqueInstance see.
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15. Singleton & UML
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16. Singleton & UML
Larman05, fig.
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