CSE360 Tutorial 06

Introduction to Software Engineering
Observer
(202206)

Transcript

1. CSE360
   Introduction to Software Engineering
   Lecture:
   Software Design Patterns - Observer
   Javier Gonzalez-Sanchez
   javiergs@asu.edu
   javiergs.engineering.asu.edu
   Office Hours: By appointment
   

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2. Previously …
   

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3. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 3
   The SOLID Principles
   

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4. Design Patterns
   

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5. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 5
   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).
   

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6. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 6
   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
   

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7. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 7
   Observer
   

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8. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 8
   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();
   }
   }
   

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9. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 9
   Subject
   abstract class Subject {
   private List _observers=new List();
   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();
   }
   }
   }
   

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10. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 10
    ConcreteSubject
    class ConcreteSubject extends Subject {
    private String _subjectState;
    public String getState {
    return _subjectState;
    }
    public void setState (value) {
    _subjectState = value;
    }
    }
    

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11. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 11
    Observer
    abstract class Observer {
    public abstract void update();
    }
    

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12. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 12
    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; }
    }
    

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13. Java Implementation
    java.util.*
    

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14. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 14
    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();
    }
    }
    

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15. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 15
    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!.. ");
    }
    }
    

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16. Example I
    

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17. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 17
    Scenario
    Student Tutor
    Classroom
    

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18. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 18
    Scenario
    Observer
    + update()
    Observable
    + addObserver()
    + notifyObservers()
    + setChanged()
    Tutor
    Student Classroom
    

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19. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 19
    Classroom
    public class Classroom {
    public static void main(String[] args) {
    Student student = new Student();
    Tutor tutor = new Tutor();
    tutor.addObserver(student);
    for (int i=0; i<5;i++)
    tutor.askQuestion();
    }
    }
    

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20. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 20
    Tutor
    import java.util.Observable;
    public class Tutor extends Observable {
    private String [] questions = { "2 + 2",
    "public or private",
    "functional or not fuctional",
    "white or black"
    };
    private String theQuestion;
    public void askQuestion() {
    theQuestion = questions[((int)(Math.random()*10))%4];
    setChanged();
    notifyObservers();
    }
    public String getQuestion() {
    return theQuestion;
    }
    }
    

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21. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 21
    Student
    import java.util.Observable;
    import java.util.Observer;
    public class Student implements Observer {
    public String answerQuestion (String question) {
    return "I am thinking about \'" + question +"\'";
    }
    @Override
    public void update(Observable o, Object arg) {
    String x = ((Tutor)o).getQuestion();
    String y = this.answerQuestion(x);
    System.out.println(y);
    }
    }
    

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22. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 22
    Output
    

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23. Example II
    

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24. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 24
    Scenario
    JFrame
    Observable
    + addObserver()
    + notifyObservers()
    + setChanged()
    Tutor
    Student Classroom
    Observer
    + update()
    JPanel
    TutorPanel
    JPanel
    

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25. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 25
    Classroom (version 2)
    import java.awt.GridLayout;
    import javax.swing.JFrame;
    public class Classroom extends JFrame {
    public Classroom() {
    Student student = new Student ();
    Tutor tutor = new Tutor();
    tutor.addObserver(student);
    setLayout(new GridLayout(2,1));
    add(student);
    add(new TutorPanel(tutor));
    }
    public static void main(String[] args) {
    JFrame window = new Classroom();
    window.setSize(500, 500);
    window.setVisible(true);
    }
    }
    

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26. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 26
    Tutor (version 2)
    import java.util.Observable;
    public class Tutor extends Observable {
    private String theQuestion;
    public void askQuestion() {
    theQuestion = questions[((int)(Math.random()*10))%4];
    setChanged();
    notifyObservers();
    }
    public void askQuestion(String s) {
    theQuestion = s;
    setChanged();
    notifyObservers();
    }
    public String getQuestion() {
    return theQuestion;
    }
    }
    

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27. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 27
    TutorPanel
    import javax.swing.*;
    import javax.awt.*;
    public class TutorPanel extends JPanel implements ActionListener{
    JTextField question = new JTextField(15);
    JButton ok = new JButton("send");
    Tutor tutor;
    public TutorPanel(Tutor tutor) {
    this.tutor = tutor;
    setBackground(Color.white);
    ImageIcon background = new ImageIcon("src/prof.png");
    JLabel label = new JLabel();
    label.setIcon(background);
    add (question);
    add (ok);
    ok.addActionListener(this);
    add(label);
    }
    @Override
    public void actionPerformed(ActionEvent e) {
    tutor.askQuestion(question.getText());
    }
    }
    

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28. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 28
    Student (version 2)
    import java.util.*;
    import javax.swing.*;
    public class Student extends JPanel implements Observer {
    JLabel label = new JLabel();
    public Student () {
    this.setBackground(Color.lightGray);
    ImageIcon background = new ImageIcon("src/student.png");
    label.setIcon(background);
    add(label);
    }
    public String answerQuestion (String question) {
    return "I am thinking about \'" + question +"\'";
    }
    @Override
    public void update(Observable o, Object arg) {
    String x = ((Tutor)o).getQuestion();
    String y = this.answerQuestion(x);
    label.setText(y);
    }
    }
    

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29. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 29
    Output
    

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30. Javier Gonzalez-Sanchez | CSE360 | Summer 2018 | 30
    Assignment 02
    

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31. CSE360 – Introduction to Software Engineering
    Javier Gonzalez-Sanchez
    javiergs@asu.edu
    Summer 2017
    Disclaimer. These slides can only be used as study material for the class CSE360 at ASU. They cannot be distributed or used for another purpose.
    

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