CSE564 Lecture 13

Software Design
Decorator
(202110)

Transcript

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

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   Previously
   

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   GoF Patterns
   

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   Singleton
   

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

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   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
   }
   }
   }
   

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   Logger
   

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   Desktop
   

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   Composite and Decorator
   

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    GoF Patterns
    

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    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.
    

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    Decorator
    

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    Practical Examples
    How Java Widgets and Containers work?
    

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    Component
    abstract class Component {
    public abstract void operation();
    }
    

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

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    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();
    }
    }
    }
    

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

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

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    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();
    }
    }
    

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    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()
    

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    Inheritance vs Decoration/Composition
    

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    Scenario
    CompanionHelper
    CompanionTroll
    Companion
    

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    Scenario
    CompanionHelper
    CompanionTroll
    Companion
    CompanionTrollHelper
    

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    Scenario
    CompanionHelper
    CompanionTroll
    Companion
    CompanionTrollHelper
    

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

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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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