decoratortheory.cs

  using System;
 
  //Decorator Pattern      Judith Bishop Dec 2006
  // Shows two decorators and the output of various
  // combinations of the decorators on the basic component
 
  interface IComponent {
    string Operation();
  }

  class Component  : IComponent {
    public string Operation () {
      return "I am walking ";
    }
  }

  class DecoratorA: IComponent {
    IComponent component;

    public DecoratorA (IComponent c) {
       component = c;
    }

    public string Operation() {
      string s = component.Operation();
      s += "and listening to Classic FM ";
      return s;
    }
  }

  class DecoratorB  : IComponent {
    IComponent component;
    public string addedState = "past the Coffee Shop ";

    public DecoratorB (IComponent c) {
      component = c;
    }

    public string Operation () {
      string s = component.Operation ();
      s += "to school ";
       return s;
    }

    public string AddedBehavior() {
      return "and I bought a cappucino ";
    }
  }

  class Client {
   
    static void Display(string s, IComponent c) {
      Console.WriteLine(s+ c.Operation());
    }

    static void Main() {
      Console.WriteLine("Decorator Pattern\n");
     
      IComponent component = new Component();
      Display("1. Basic component: ", component);
      Display("2. A-decorated : ", new DecoratorA(component));
      Display("3. B-decorated : ", new DecoratorB(component));
      Display("4. B-A-decorated : ", new DecoratorB(
           new DecoratorA(component)));
      // Explicit DecoratorB
      DecoratorB b = new DecoratorB(new Component());
      Display("5. A-B-decorated : ", new DecoratorA(b));
      //Invoking its added state and added behaviour
      Console.WriteLine("\t\t\t"+ b.addedState + b.AddedBehavior());
    }
  }

/* Output:
Decorator Pattern

1. Basic component: I am walking
2. A-decorated : I am walking and listening to Classic FM
3. B-decorated : I am walking to school
4. B-A-decorated : I am walking and listening to Classic FM to school
5. A-B-decorated : I am walking to school and listening to Classic FM
      past the Coffee Shop and I bought a cappucino
*/