CSE360 Lecture 17

Introduction to Software Engineering
Software Design Patterns
(201806)

Transcript

1. CSE360 Introduction to Software Engineering Lecture 17: Software Design Patterns: Observer Javier Gonzalez-Sanchez javiergs@asu.edu javiergs.engineering.asu.edu Office Hours: By appointment
2. Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 2 Definition • Design patterns are solutions to software design problems you find again and again in real-world application development. • Patterns are about reusable designs and interactions of objects. • The 23 Gang of Four (GoF) patterns are generally considered the foundation for all other patterns (Gamma, Helm, Johnson, and Vlissides).
3. Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 3 GoF Patterns Creational Patterns • Abstract Factory • Builder • Factory Method • Prototype • Singleton Structural Patterns • Adapter • Bridge • Composite • Decorator • Façade • Flyweight • Proxy Behavioral Patterns • Chain of Responsibility • Command • Interpreter • Iterator • Mediator • Memento • Observer • State • Strategy • Template Method • Visitor
4. Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 4 Observer
5. Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 5 Observer Public class MainApp{ public static void Main() { // Configure Observer pattern ConcreteSubject s = new ConcreteSubject(); s.Attach(new ConcreteObserver(s, "X")); s.Attach(new ConcreteObserver(s, "Y")); s.Attach(new ConcreteObserver(s, "Z")); // Change subject and notify observers s.SubjectState = "ABC"; s.Notify(); } }
6. Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 6 Subject abstract class Subject { private List<Observer> _observers=new List<Observer>(); public void Attach(Observer observer) { _observers.Add(observer); } public void Detach(Observer observer){ _observers.Remove(observer); } public void Notify(){ foreach (Observer o in _observers){ o.Update(); } } }
7. Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 7 ConcreteSubject class ConcreteSubject extends Subject { private String _subjectState; public String getState { return _subjectState; } public void setState (value) { _subjectState = value; } }
8. Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 8 Observer abstract class Observer { public abstract void update(); }
9. Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 9 ConcreteObserver class ConcreteObserver extends Observer { private string _name; private string _observerState; private ConcreteSubject _subject; // Constructor public ConcreteObserver(ConcreteSubject s, string n){ this._subject = s; this._name = n; } public override void update() { _observerState = _subject.SubjectState; println("Observer %s's new state is $s", _name, _observerState); } public Subject getSubject() { return _subject; } public void setSubject(Subject value) { _subject = value; } }
10. Java Implementation java.util.*
11. Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 11 Java Subject (Observable) import java.util.Observable; public class ObservableDemo extends Observable { private String weather; public ObservableDemo(String weather) { this.weather = weather; } public String getWeather() { return weather; } public void setWeather(String weather) { this.weather = weather; setChanged(); notifyObservers(); } }
12. Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 12 Java Observer (Observer) import java.util.Observable; import java.util.Observer; public class ObserverExample implements Observer { private ObservableDemo weatherUpdate ; @Override public void update(Observable observable, Object arg) { weatherUpdate = (ObservableDemo) observable; System.out.println("Weather Report Live. Its "+weatherUpdate.getWeather()); } public static void main(String[] args) { ObservableDemo observable = new ObservableDemo(null); ObserverExample observer = new ObserverExample(); observable.addObserver(observer); observable.setWeather("Bright and sunny... "); observable.setWeather("Raining Heavily!.. "); } }
13. CSE360 – Introduction to Software Engineering Javier G onzalez-Sanchez javiergs@ asu.edu Sum m er 2017 Disclaim er. These slides can only be used as study m aterial for the class C SE360 at ASU. They cannot be distributed or used for another purpose.