CSE460 Lecture 13

Software Analysis and Design
Observer
(202102)

Transcript

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   CSE 460
   Software Analysis and Design
   Lecture 13: Observer
   Dr. Javier Gonzalez-Sanchez
   javiergs@asu.edu
   javiergs.engineering.asu.edu | javiergs.com
   PERALTA 230U
   Office Hours: By appointment
   

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   Previously …
   Design Patterns
   

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   00000001
   GoF Patterns
   

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   00000001
   Observer
   

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   00000001
   Observer
   

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   Java Implementation
   java.util.*
   

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   00000001
   Scenario
   Observer
   + update()
   Observable
   + addObserver()
   + notifyObservers()
   + setChanged()
   Tutor
   Student Classroom
   

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   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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   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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    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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    Output
    

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    Example 2
    Observer
    

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    00000001
    Scenario
    JFrame
    Observable
    + addObserver()
    + notifyObservers()
    + setChanged()
    Tutor
    Student Classroom
    Observer
    + update()
    JPanel
    TutorPanel
    JPanel
    

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    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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    00000001
    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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    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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    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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    Output
    

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    Example 3
    Observer
    

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    00000001
    Observer - Steps
    

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    Source
    

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    00000001
    Boss
    

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    NoteTaker
    

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    World
    

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    CSE 460 Software Analysis and Design
    Javier Gonzalez-Sanchez
    javiergs@asu.edu
    Fall 2020
    Disclaimer. These slides can only be used as study material for the class CSE460 at ASU. They cannot be distributed or used for another purpose.
    

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