jgs CSE 460 Software Analysis and Design Lecture 18: Additional Design Patterns Dr. Javier Gonzalez-Sanchez [email protected] javiergs.engineering.asu.edu | javiergs.com PERALTA 230U Office Hours: By appointment 

jgs 460 00010010 Announcement § Quiz 05 is due tonight. It opens at the end of the lecture 

jgs 460 00010010 Singleton 

jgs 460 00010010 Singleton class Main { public static void main(String []a){ // Constructor is protected -- cannot use new Singleton s1 = Singleton.getInstance(); Singleton s2 = Singleton.getInstance(); // Test for same instance if (s1 == s2){ // true - Objects are the same instance } } } 

jgs 460 00010010 Singleton class Singleton{ private static Singleton instance; // Constructor is 'protected' protected Singleton() {} public static Singleton getInstance(){ if (instance == null){ instance = new Singleton(); } return instance; } } 

jgs 460 00010010 Practice 

jgs 460 00010010 A Singleton 

jgs 460 00010010 Add More Objects 

jgs 460 00010010 Previously … 

jgs 460 00010010 Next 

jgs 460 00010010 Chain of Responsibilities, Factory, Adapter 

jgs Chain of Responsibility Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. 

jgs 460 00010010 Chain of Responsibility 

jgs 460 00010010 Chain of Responsibility vs Composite vs Decorator 

jgs 460 00010010 Chain of Responsibility public class Client { public static void main(String[] args) { // Setup Chain of Responsibility ConcreteHandler2 h1 = new ConcreteHandler2(); ConcreteHandler2 h2 = new ConcreteHandler2(); ConcreteHandler1 h3 = new ConcreteHandler1(); h1.setSuccessor(h2); h2.setSuccessor(h3); // Generate and process request int[] requests = { 2, 5, 14, 22, 18, 3, 27, 20 }; for (int i = 0; i < requests.length; i++) { h1.HandleRequest(requests[i]); } } } 

jgs 460 00010010 Handler abstract class Handler { public abstract void HandleRequest(int request); } 

jgs 460 00010010 ConcreteHandler1 class ConcreteHandler1 extends Handler { public void HandleRequest(int request) { System.out.println("I am the last in line"); } } 

jgs 460 00010010 ConcreteHandler2 class ConcreteHandler2 extends Handler { protected Handler successor; public void setSuccessor(Handler successor) { this.successor = successor; } public void HandleRequest(int request) { if (request >= 10 && request < 20) { // code here System.out.println("I am the handling it"); } else if (successor != null) { System.out.println("Passing it..."); successor.HandleRequest(request); } } } 

jgs Factory Wrapper of a constructor One entire object to be built in a single method call 

jgs 460 00010010 Next 

jgs 460 00010010 Abstract Factory 

jgs 460 00010010 Products public interface Shape { void draw(); } public class RoundedRectangle implements Shape { public void draw() { System.out.println("Inside RoundedRectangle/draw() method."); } } public class RoundedSquare implements Shape { public void draw() { System.out.println("Inside RoundedSquare/draw() method."); } } public class Rectangle implements Shape { public void draw() { System.out.println("Inside Rectangle/draw() method."); } } 

jgs 460 00010010 Factories public abstract class AbstractFactory { Shape getShape(String shapeType) {} } public class ShapeFactory extends AbstractFactory { public Shape getShape(String shapeType){ if(shapeType.equalsIgnoreCase("RECTANGLE")){ return new Rectangle(); }else if(shapeType.equalsIgnoreCase("SQUARE")){ return new Square(); } return null; } } 

jgs 460 00010010 Factories public class RoundedShapeFactory extends AbstractFactory { public Shape getShape(String shapeType){ if(shapeType.equalsIgnoreCase("RECTANGLE")){ return new RoundedRectangle(); }else if(shapeType.equalsIgnoreCase("SQUARE")){ return new RoundedSquare(); } return null; } } 

jgs 460 00010010 Client public class Client { public static void main(String[] args) { AbstractFactory shapeFactory = new ShapeFactory(); //get an object of Shape Rectangle Shape shape1 = shapeFactory.getShape("RECTANGLE"); //call draw method of Shape Rectangle shape1.draw(); //get an object of Shape Square Shape shape2 = shapeFactory.getShape("SQUARE"); //call draw method of Shape Square shape2.draw(); ] //get shape factory AbstractFactory shapeFactory1 = new RoundedShapeFactory(); //get an object of Shape Rectangle Shape shape3 = shapeFactory1.getShape("RECTANGLE"); //call draw method of Shape Rectangle shape3.draw(); //get an object of Shape Square Shape shape4 = shapeFactory1.getShape("SQUARE"); //call draw method of Shape Square shape4.draw(); } } 

jgs CSE 460 Software Analysis and Design Javier Gonzalez-Sanchez [email protected] 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.