CSE564 Lecture 12

Software Design
Singleton
(202109)

Transcript

1. jgs
   CSE 564
   Software Design
   Lecture 11: Design Patterns - Singleton
   Dr. Javier Gonzalez-Sanchez
   javiergs@asu.edu
   javiergs.engineering.asu.edu | javiergs.com
   PERALTA 230U
   Office Hours: By appointment
   

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2. jgs
   Example 2
   Observer
   

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3. Javier Gonzalez-Sanchez | CSE564 | Fall 2020 | 4
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   Scenario
   JFrame
   Observable
   + addObserver()
   + notifyObservers()
   + setChanged()
   Tutor
   Student Classroom
   Observer
   + update()
   JPanel
   TutorPanel
   JPanel
   

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4. Javier Gonzalez-Sanchez | CSE564 | Fall 2020 | 5
   jgs
   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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5. Javier Gonzalez-Sanchez | CSE564 | Fall 2020 | 6
   jgs
   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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6. Javier Gonzalez-Sanchez | CSE564 | Fall 2020 | 7
   jgs
   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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7. Javier Gonzalez-Sanchez | CSE564 | Fall 2020 | 8
   jgs
   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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8. Javier Gonzalez-Sanchez | CSE564 | Fall 2020 | 9
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   Output
   

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9. jgs
   Singleton
   

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10. Javier Gonzalez-Sanchez | CSE564 | Fall 2020 | 11
    jgs
    GoF Patterns
    

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11. Javier Gonzalez-Sanchez | CSE564 | Fall 2020 | 12
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    Singleton
    

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12. Javier Gonzalez-Sanchez | CSE564 | Fall 2020 | 13
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    Singleton
    class MainApp {
    public static void Main(String []a){
    // Constructor is protected -- cannot use new
    Singleton s1 = Singleton.getInstance();
    Singleton s2 = Singleton.getInstance();
    // Test for same instance
    if (s1 == s2){
    // true - Objects are the same instance
    }
    }
    }
    

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13. Javier Gonzalez-Sanchez | CSE564 | Fall 2020 | 14
    jgs
    Singleton
    class Singleton{
    private static Singleton _instance;
    // Constructor is 'protected'
    protected Singleton() {}
    public static Singleton getInstance(){
    if (_instance == null){
    _instance = new Singleton();
    }
    return _instance;
    }
    }
    

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14. Javier Gonzalez-Sanchez | CSE564 | Fall 2020 | 15
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    Scenario
    Quiz
    Tutor
    System
    Companion
    ControlCenter
    << singleton>>
    

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15. jgs
    Decorator
    To be Continued …
    

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16. jgs
    CSE 564 Computer Systems Fundamentals
    Javier Gonzalez-Sanchez
    javiergs@asu.edu
    Fall 2020
    Disclaimer. These slides can only be used as study material for the class CSE564 at ASU. They cannot be distributed or used for another purpose.
    

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