jgs CSE 564 Software Design Lecture 09: Design Patterns Dr. Javier Gonzalez-Sanchez [email protected] javiergs.engineering.asu.edu | javiergs.com PERALTA 230U Office Hours: By appointment 

jgs 564 00001000 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: 

jgs Previously Object-Oriented Design and Programming 

jgs 564 00001000 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) 

jgs 564 00001000 DIP Example What about ISP? 

jgs Patterns Software Design 

jgs 564 00001000 Not Everything that Can be … Should be … 

jgs 564 00001000 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). 

jgs 564 00001000 Timeline 1989 Beck OO Thinking Architecture 1993 Gamma et al. GoF Patterns 1994 

jgs 564 00001000 GoF Patterns 

jgs 564 00001000 GoF Patterns 

jgs Observer Software Design 

jgs 564 00001000 Observer 

jgs 564 00001000 Observer 

jgs 564 00001000 Observer 

jgs 564 00001000 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); } } } 

jgs 564 00001000 Observer public abstract class Observer { public abstract void update(Subject s); } 

jgs 564 00001000 ConcreteSubject class ConcreteSubject extends Subject { private String data; public String getData() { return data; } public void setData(String s) { data = s; notifying(); } } 

jgs 564 00001000 ConcreteObserver class ConcreteObserver extends Observer { @Override public void update(Subject s) { String info = ((ConcreteSubject)s).getData(); System.out.println("Subject is doing this: "+info); } } 

jgs 564 00001000 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"); } } 

jgs 564 00001000 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"); } } 

jgs 564 00001000 Observer 

jgs 564 00001000 Questions about Observer 

jgs CSE 564 Software Design Javier Gonzalez-Sanchez, Ph.D. [email protected] 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.