CSC307 Lecture 10

Introduction to Software Engineering
Design Patterns I
(202307)

Transcript

1. jgs CSC 307 Introduction to Software Engineering Lecture 10: Design Patterns Dr. Javier Gonzalez-Sanchez javiergs@calpoly.edu www.javiergs.com Building 14 -227 Office Hours: By appointment
2. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 3 public class A extends B { C c1, c2; public A() { c1 = new C(); } public void method() { D d = new D(); d.working(); } } Public class X { public void m() { B var = new A(); double x = Math.sqrt(5); } } public class B implements E { public B() { C c1 = new C(); } public void method() { B b = new B(); b.sleep(); } } public class Y { A [] a = new A[5]; } Review
3. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 4 Quiz 02
4. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 5 Assignment 01
5. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 6 Assignment 01 https://blockly-spiderworld.sourceforge.io/appengine/spider.html
6. jgs Design
7. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 8 Not Everything that Can be … Should be …
8. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 9 § 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 between objects. § The 23 Gang of Four (GoF) patterns are generally considered the foundation for all other patterns (Gamma, Helm, Johnson, and Vlissides). Definition
9. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 10 Timeline 1989 Beck OO Thinking 1993 Gamma et al. GoF Patterns
10. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 11 App
11. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 12 Class Diagram
12. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 13 Key Idea Single Responsibility Principle
13. jgs Observer
14. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 15 Observer
15. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 16 Observer
16. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 17 class Student { public String answerQuestion (String question) { String answer; // solve the question return answer; } } Student
17. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 18 class Teacher { private String question; public String getQuestion() { return question; } public void createQuestion () { question = // AI to create a question here } } Teacher
18. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 19 public abstract class Observer { public abstract void update(Observable s); } Observer
19. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 20 import java.util.LinkedList; public abstract class Observable { private LinkedList<Observer> observers = new LinkedList<Observer>(); public void addObserver(Observer observer) { observers.add(observer); } public void removeObserver(Observer observer) { observers.remove(observer); } public void notifying() { for (Observer ob : observers) { ob.update(this); } } } Observable
20. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 21 class Student extends Observer { public String answerQuestion (String question) { String answer; // solve the question return answer; } @Override public void update(Observable s) { String q = ((Teacher)s).getQuestion(); Sting answer = answerQuestion (q); System.out.println (answer); } } Student as Observer
21. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 22 class Teacher extends Observable { private String question; public String getQuestion() { return question; } public void createQuestion () { question = // AI to create a question here notifying(); } } Teacher as Observable
22. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 23 public class Main { public static void main(String[]a) { Teacher teacher = new Teacher(); Student s1 = new Student(); Student s2 = new Student(); teacher.addObserver(s1); teacher.addObserver(s2); // Teaching teacher.createQuestion(); // More Teaching teacher.createQuestion(); } } Main
23. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 24 Scenario Observer + update() Observable + addObserver() + notifyObservers() + setChanged() Teacher Student Main
24. jgs Java Implementation java.util.*
25. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 26 Scenario Observer + update() Observable + addObserver() + notifyObservers() + setChanged() Teacher Student Main
26. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 27 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
27. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 28 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
28. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 29 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
29. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 30 Output
30. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 31 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.
31. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 61 Questions
32. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 62 Office Hours Tuesday and Thursday 3 - 5 pm But an appointment required Sent me an email – javiergs@calpoly.edu
33. jgs
34. jgs CSC 307 Introduction to Software Engineering Lab 10: Design Patterns Dr. Javier Gonzalez-Sanchez javiergs@calpoly.edu www.javiergs.com Building 14 -227 Office Hours: By appointment
35. jgs Javier Gonzalez-Sanchez | CSC 308 | Winter 2023 | 65 Scenario
36. jgs CSC 307 Introduction to Software Engineering Javier Gonzalez-Sanchez, Ph.D. javiergs@calpoly.edu Summer 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.