Design Patterns

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REQUIREMENTS (2) • When the name of a file or directory is changed (setName), the representation of the name on the display will be updated, too. Applicability Use the Observer pattern when • change to one object requires changing others, and you do not know how many objects need to be changed. • an object should be able to notify other objects without making assumptions about who these objects are. 45 47 EXAMPLE: “OBSERVER” Classification object/behavioral Intent Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. Also Known As Dependents, Publish-Subscribe Structure Subject Attach(Observer) Detach(Observer) Notify() ConcreteSubject subjectState GetState() SetState() observers 46 48 subject Observer Update() ConcreteObserver observerState Update()
Participants • Subject – knows its observers – provides an interface for attaching and detaching Observer objects • Observer – defines an update interface for objects that should be notified of changes in a subject APPLICATION OF THE OBSERVER PATTERN Subject Attach(Observer) Detach(Observer) Notify() File GetName() SetName() observers 49 Observer Update() concreteSubject concreteObserver filename subject obsStateOfFilename 51 Display Update() • ConcreteSubject – stores state of interest to ConcreteObserver object – sends a notification to its observers when its state changes • ConcreteObserver – maintains a reference to a ConcreteSubject object – stores state that should stay consistent with the ConcreteSubject’s – implements the update-interface of Observer Related <strong>Patterns</strong> Mediator, Singleton REQUIREMENTS (3) • It is not allowed to delete directories which include files or are write protected. 50 52
Page 1 and 2: Design Patterns DESIGN PATTERNS: CH
Page 3 and 4: ASSOCIATIONS ➠ denote the relatio
Page 5 and 6: Classifying, Describing, and Using
Page 7 and 8: HOW MVC WORKS - AN OVERVIEW MVC CLA
Page 9 and 10: • Composite (picture) - defines b
Page 11: Known Uses • View-class in Model/
Page 15 and 16: APPLICATION OF THE STRATEGY PATTERN
Page 17: ➠ We have presented and used the

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