CSE360 Introduction to Software Engineering Lecture 19: Software Design Patterns: Singleton and Decorator Javier Gonzalez-Sanchez [email protected] javiergs.engineering.asu.edu Office Hours: By appointment

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 2 GoF Patterns Creational Patterns • Abstract Factory • Builder • Factory Method • Prototype • Singleton Structural Patterns • Adapter • Bridge • Composite • Decorator • Façade • Flyweight • Proxy Behavioral Patterns • Chain of Responsibility • Command • Interpreter • Iterator • Mediator • Memento • Observer • State • Strategy • Template Method • Visitor

Singleton

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 4 Singleton

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 5 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 } } }

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 6 Singleton class Singleton{ private static Singleton _instance; // Constructor is 'protected' protected Singleton() {} public static Singleton getInstance(){ if (_instance == null){ _instance = new Singleton(); } return _instance; } }

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 7 Scenario Quiz Tutor System Companion ControlCenter << singleton>>

Decorator

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 9 GoF Patterns Creational Patterns • Abstract Factory • Builder • Factory Method • Prototype • Singleton Structural Patterns • Adapter • Bridge • Composite • Decorator • Façade • Flyweight • Proxy Behavioral Patterns • Chain of Responsibility • Command • Interpreter • Iterator • Mediator • Memento • Observer • State • Strategy • Template Method • Visitor

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 10 Decorator

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 11 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(); } }

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 12 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()

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 13 Component abstract class Component { public abstract void operation(); }

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 14 ConcreteComponent class ConcreteComponent extends Component { @override public void Operation() { System.out.print("ConcreteComponent-Operation()"); } }

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 15 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(); } } }

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 16 ConcreteDecoratorA class ConcreteDecoratorA extends Decorator { @override public void operation() { super.operation(); System.out.println("ConcreteDecoratorA-Operation()”); } }

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 17 ConcreteDecoratorB class ConcreteDecoratorB extends Decorator { @override public void operation() { super.operation(); addedBehavior(); System.out.println("ConcreteDecoratorB-Operation()"); } void addedBehavior() { } }

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 18 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.

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 19 Scenario CompanionHelper CompanionTroll Companion

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 20 Scenario CompanionHelper CompanionTroll Companion CompanionTrollHelper

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 21 Scenario CompanionHelper CompanionTroll Companion CompanionTrollHelper

Javier Gonzalez-Sanchez | CSE360 | Summer 2017 | 22 Decorator WhiteBody body = new WhiteBody(); Mask mask = new Mask(); Helmet helmet = new Helmet(); // Link decorators mask.SetComponent(body); helmet.SetComponent(mask); helmet.Operation();

CSE360 – Introduction to Software Engineering Javier G onzalez-Sanchez javiergs@ asu.edu Sum m er 2017 Disclaim er. These slides can only be used as study m aterial for the class C SE360 at ASU. They cannot be distributed or used for another purpose.