CSE460 Lecture 12

Software Analysis and Design
Design Patterns
(202102)

Transcript

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   CSE 460
   Software Analysis and Design
   Lecture 12: Design Patterns
   Dr. Javier Gonzalez-Sanchez
   javiergs@asu.edu
   javiergs.engineering.asu.edu | javiergs.com
   PERALTA 230U
   Office Hours: By appointment
   

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   Announcement
   § Quiz 04 is due Today (midnight) 11:59 PM AZ time.
   

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   The LEGO Paradigm
   

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   Patterns are these Blocks
   § 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).
   

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   GoF Patterns
   

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   GoF Patterns
   

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   Observer
   Software Design
   

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   Observer
   

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    Observer
    

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

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    ConcreteObserver
    class ConcreteObserver extends Observer {
    private string name;
    private string observerState;
    private ConcreteSubject subject;
    public Subject getSubject() { return subject; }
    public void setSubject(Subject s) { subject = s; }
    // Constructor
    public ConcreteObserver(ConcreteSubject s, string n){
    this.subject = s;
    this.name = n;
    }
    public override void update() {
    observerState = subject.subjectState;
    println("Observer %s's new state is %s", name, observerState);
    }
    }
    

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    Subject
    abstract class Subject {
    private List observers = new List();
    public void attach(Observer observer) {
    observers.add(observer);
    }
    public void detach(Observer observer){
    observers.remove(observer);
    }
    public void notify(){
    foreach (Observer o in observers){
    o.update();
    }
    }
    }
    

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    ConcreteSubject
    class ConcreteSubject extends Subject {
    private String subjectState;
    public String getState () {
    return subjectState;
    }
    public void setState (s) {
    subjectState = s;
    }
    }
    

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    Main
    Public class Main {
    public static void Main() {
    // Configure Observer pattern
    ConcreteSubject s = new ConcreteSubject();
    ConcreteObserver eyeOne = new ConcreteObserver(s, "X");
    ConcreteObserver eyeTwo = new ConcreteObserver(s, "X");
    s.Attach(eyeOne);
    s.Attach(eyeTwo);
    // Change subject and notify observers
    s.subjectState = "ABC";
    s.notify();
    }
    }
    

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    Java Implementation
    java.util.*
    

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    Scenario
    Student Tutor
    Classroom
    

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    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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    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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