CSE564 Lecture 09

Software Design
Design Patterns: Observer
(202102)

Transcript

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   CSE 564
   Software Design
   Lecture 09: 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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   Homework
   Read:
   § Design Patterns: Abstraction and Reuse of Object-Oriented Design
   Gamma, Helm, Johnson, Vlissides
   § European Conference on Object-Oriented Programming
   October 1993
   § This will become:
   

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   Previously
   Object-Oriented Design and Programming
   

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   Design Principles
   There are five key design principles to consider in Object-Oriented:
   § Single Responsibility Principle (SRP)
   § Open-Closed Principle (OCP)
   § Liskov Substitution Principle (LSP)
   § Interface Segregation Principle (ISP)
   § Dependency Inversion Principle (DIP)
   

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   DIP Example
   What about ISP?
   

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   Patterns
   Software Design
   

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   Not Everything that Can be … Should be …
   

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   Definition
   § 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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   Timeline
   1989 Beck
   OO Thinking
   Architecture
   1993 Gamma et al.
   GoF Patterns
   1994
   

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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
    

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    Subject
    import java.util.LinkedList;
    public abstract class Subject {
    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);
    }
    }
    }
    

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

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    ConcreteSubject
    class ConcreteSubject extends Subject {
    private String data;
    public String getData() {
    return data;
    }
    public void setData(String s) {
    data = s;
    notifying();
    }
    }
    

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    ConcreteObserver
    class ConcreteObserver extends Observer {
    @Override
    public void update(Subject s) {
    String info = ((ConcreteSubject)s).getData();
    System.out.println("Subject is doing this: "+info);
    }
    }
    

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    Main
    public class Main {
    public static void main(String[]a) {
    // Configure pattern
    ConcreteSubject s = new ConcreteSubject();
    ConcreteObserver eyeOne = new ConcreteObserver();
    ConcreteObserver eyeTwo = new ConcreteObserver();
    s.addObserver(eyeOne);
    s.addObserver(eyeTwo);
    // Change subject
    s.setData("ABC");
    s.setData("XYZ");
    }
    }
    

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    Main
    public class Main {
    public static void main(String[]a) {
    // Configure pattern
    ConcreteSubject s = new ConcreteSubject();
    ConcreteObserver eyeOne = new ConcreteObserver();
    ConcreteObserver eyeTwo = new ConcreteObserver();
    s.addObserver(eyeOne);
    s.addObserver(eyeTwo);
    // Change subject
    s.setData("ABC");
    s.setData("XYZ");
    }
    }
    

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    Observer
    

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    Questions about Observer
    

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    CSE 564 Software Design
    Javier Gonzalez-Sanchez, Ph.D.
    javiergs@asu.edu
    Fall 2021
    Copyright. 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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