CSC307 Lecture 10

Introduction to Software Engineering
Design Patterns I
(202307)

Transcript

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   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
   

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   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
   

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   Quiz 02
   

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   Assignment 01
   

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   Assignment 01
   https://blockly-spiderworld.sourceforge.io/appengine/spider.html
   

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   Design
   

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   Not Everything that Can be … Should be …
   

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   § 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
   

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   Timeline
   1989 Beck
   OO Thinking
   1993 Gamma et al.
   GoF Patterns
   

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    App
    

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    Class Diagram
    

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    Key Idea
    Single Responsibility
    Principle
    

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    Observer
    

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    Observer
    

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    Observer
    

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    class Student {
    public String answerQuestion (String question) {
    String answer;
    // solve the question
    return answer;
    }
    }
    Student
    

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    class Teacher {
    private String question;
    public String getQuestion() {
    return question;
    }
    public void createQuestion () {
    question = // AI to create a question here
    }
    }
    Teacher
    

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    public abstract class Observer {
    public abstract void update(Observable s);
    }
    Observer
    

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    import java.util.LinkedList;
    public abstract class Observable {
    private LinkedList observers = new LinkedList();
    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
    

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    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
    

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    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
    

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    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
    

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

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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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    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 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
    

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    Scenario
    

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    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.
    

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