jgs CSC 308 Software Engineering 1 Lecture 14: Design Patterns - Observer Dr. Javier Gonzalez-Sanchez [email protected] www.javiergs.com Building 14 -227 

jgs Previously … 

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

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 4 Scenario Observer + update() Observable + addObserver() + notifyObservers() + setChanged() Teacher Student Main 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 5 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 

jgs Java Implementation java.util.* 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 7 Scenario Observer + update() Observable + addObserver() + notifyObservers() + setChanged() Teacher Student Main 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 8 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 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 9 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 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 10 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 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 11 Output 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 12 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. 

jgs Test Yourselves 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 14 Output 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 15 Scenario A JFrame Observable + addObserver() + notifyObservers() + setChanged() Tutor Student Classroom Observer + update() JPanel TutorPanel JPanel 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 16 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) 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 17 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) 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 18 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 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 19 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) 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 20 Scenario B JFrame Observable + addObserver() + notifyObservers() + setChanged() TutorBrain StudentBrain Classroom Observer + update() JPanel TutorPanel JPanel StudentPanel 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 21 Scenario 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 22 Questions 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 23 Office Hours Tuesday and Thursday 3 - 5 pm But an appointment required Sent me an email – [email protected] 

jgs 

jgs CSC 308 Software Engineering 1 Lab 14: … Dr. Javier Gonzalez-Sanchez [email protected] www.javiergs.com Building 14 -227 Office Hours: By appointment 

jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 26 Ideas No Lab Today But you have a Quiz instead. It is due today before midnight. 

jgs CSC 308 Software Engineering I Javier Gonzalez-Sanchez, Ph.D. [email protected] 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.