jgs CSE 564 Software Design Lecture 13: Design Patterns - Decorator Dr. Javier Gonzalez-Sanchez [email protected] javiergs.engineering.asu.edu | javiergs.com PERALTA 230U Office Hours: By appointment 

jgs Previously 

jgs 564 00001101 GoF Patterns 

jgs 564 00001101 Singleton 

jgs 564 00001101 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 564 00001101 Singleton class MainApp { 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 564 00001101 Logger 

jgs 564 00001101 Desktop 

jgs Composite and Decorator 

jgs 564 00001101 GoF Patterns 

jgs 564 00001101 Decorator vs Inheritance § Both allow you to change how an object behaves § The decorator pattern can be used to make it possible to extend (decorate) the functionality of a certain object at runtime. § Inheritance adds behavior at compilation-time. 

jgs 564 00001101 Decorator 

jgs 564 00001101 Practical Examples How Java Widgets and Containers work? 

jgs 564 00001101 Component abstract class Component { public abstract void operation(); } 

jgs 564 00001101 ConcreteComponent class ConcreteComponent extends Component { @override public void operation() { System.out.print("ConcreteComponent-Operation()"); } } 

jgs 564 00001101 Decorator abstract class Decorator extends Component { protected Component component; public void setComponent(Component component) { this.component = component; } @override public void operation() { if (component != null) { component.operation(); } } } 

jgs 564 00001101 ConcreteDecoratorA class ConcreteDecoratorA extends Decorator { @override public void operation() { super.operation(); System.out.println("ConcreteDecoratorA-Operation()”); } } 

jgs 564 00001101 ConcreteDecoratorB class ConcreteDecoratorB extends Decorator { @override public void operation() { super.operation(); addedBehavior(); System.out.println("ConcreteDecoratorB-Operation()"); } void addedBehavior() { } } 

jgs 564 00001101 Main class MainApp { static void main() { // Create ConcreteComponent and two Decorators ConcreteComponent c = new ConcreteComponent(); ConcreteDecoratorA d1 = new ConcreteDecoratorA(); ConcreteDecoratorB d2 = new ConcreteDecoratorB(); // Link decorators d1.SetComponent(c); d2.SetComponent(d1); d2.Operation(); } } 

jgs 564 00001101 Main class MainApp { static void main() { // Create ConcreteComponent and two Decorators ConcreteComponent c = new ConcreteComponent(); ConcreteDecoratorA d1 = new ConcreteDecoratorA(); ConcreteDecoratorB d2 = new ConcreteDecoratorB(); // Link decorators d1.SetComponent(c); d2.SetComponent(d1); d2.Operation(); } } ConcreteComponent - Operation() ConcreteDecoratorA - Operation() ConcreteDecoratorB - Operation() 

jgs Inheritance vs Decoration/Composition 

jgs 564 00001101 Scenario CompanionHelper CompanionTroll Companion 

jgs 564 00001101 Scenario CompanionHelper CompanionTroll Companion CompanionTrollHelper 

jgs 564 00001101 Scenario CompanionHelper CompanionTroll Companion CompanionTrollHelper 

jgs 564 00001101 Decorator WhiteBody body = new WhiteBody(); Mask mask = new Mask(); Helmet helmet = new Helmet(); // Link decorators mask.SetComponent(body); helmet.SetComponent(mask); helmet.Operation(); 

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.