CSC308 Lecture 14

Software Engineering I
Design Patterns - Observer
(202302)

Transcript

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   CSC 308
   Software Engineering 1
   Lecture 14:
   Design Patterns - Observer
   Dr. Javier Gonzalez-Sanchez
   javiergs@calpoly.edu
   www.javiergs.com
   Building 14 -227
   

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   Previously …
   

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   Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 3
   GoF Patterns
   

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   Scenario
   Observer
   + update()
   Observable
   + addObserver()
   + notifyObservers()
   + setChanged()
   Teacher
   Student Main
   

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   public class Main {
   public static void main(String[]a) {
   Teacher teacher1 = new Teacher();
   Teacher teacher2 = new Teacher();
   Student s1 = new Student();
   Student s2 = new Student();
   teacher1.addObserver(s1);
   teacher2.addObserver(s2);
   teacher1.addObserver(s1);
   teacher2.addObserver(s2);
   teacher1.createQuestion();
   teacher2.createQuestion();
   }
   }
   Scenario
   

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   Java Implementation
   java.util.*
   

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   Scenario
   Observer
   + update()
   Observable
   + addObserver()
   + notifyObservers()
   + setChanged()
   Teacher
   Student Main
   

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   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);
   }
   }
   Student
   

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   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;
   }
   }
   Tutor
   

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    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();
    }
    }
    Classroom
    

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    Output
    

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    Java API
    Java 9 deprecated Observer and Observable
    implementation in java.util package.
    It deprecated its own implementation of the
    concept, not the concept itself
    Why? serialization and thread safety problems.
    Solution: PropertyChangeListener from
    java.beans package.
    

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    Test Yourselves
    

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    Output
    

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    Scenario A
    JFrame
    Observable
    + addObserver()
    + notifyObservers()
    + setChanged()
    Tutor
    Student Classroom
    Observer
    + update()
    JPanel
    TutorPanel
    JPanel
    

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    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);
    }
    }
    Student (version 2)
    

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    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;
    }
    }
    Tutor (version 2)
    

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    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());
    }
    }
    TutorPanel
    

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    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);
    }
    }
    Classroom (version 2)
    

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    Scenario B
    JFrame
    Observable
    + addObserver()
    + notifyObservers()
    + setChanged()
    TutorBrain
    StudentBrain Classroom
    Observer
    + update()
    JPanel
    TutorPanel
    JPanel
    StudentPanel
    

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    Scenario
    

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    Questions
    

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    Office Hours
    Tuesday and Thursday 3 - 5 pm
    But an appointment required
    Sent me an email – javiergs@calpoly.edu
    

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    CSC 308
    Software Engineering 1
    Lab 14:
    …
    Dr. Javier Gonzalez-Sanchez
    javiergs@calpoly.edu
    www.javiergs.com
    Building 14 -227
    Office Hours: By appointment
    

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    Ideas
    No Lab Today
    But you have a Quiz instead.
    It is due today before midnight.
    

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    CSC 308 Software Engineering I
    Javier Gonzalez-Sanchez, Ph.D.
    javiergs@calpoly.edu
    Winter 2023
    Copyright. These slides can only be used as study material for the class CSC308 at Cal Poly.
    They cannot be distributed or used for another purpose.
    

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