Decorator Pattern question C# / java -

i looking @ this wikipedia article, , couldn't understand how hell working. little bit frustrated not being able understand code looking @ it, dedided port code c# (i'm .net, sorry guys :)). minor modifications needed (inherits , extends, base super, etc) , run app. surprise, got following output :

cost: 1 ingredient: coffee cost: 1 ingredient: coffee cost: 1 ingredient: coffee cost: 1 ingredient: coffee 

just curious, can java dev tell me what's different here , why wikipedia example works (if work does, of course).

    namespace consoleapplication1 {  class program  {   static void main(string[] args)   {    coffee samplecoffee = new simplecoffee();   console.writeline("cost: " + samplecoffee.getcost() + " ingredient: " + samplecoffee.getingredient());          samplecoffee = new milk(samplecoffee);         console.writeline("cost: " + samplecoffee.getcost() + " ingredient: " + samplecoffee.getingredient());          samplecoffee = new sprinkles(samplecoffee);         console.writeline("cost: " + samplecoffee.getcost() + " ingredient: " + samplecoffee.getingredient());          samplecoffee = new whip(samplecoffee);         console.writeline("cost: " + samplecoffee.getcost() + " ingredient: " + samplecoffee.getingredient());     console.readkey();    }  }    //the coffee interface defines functionality of coffee implemented decorator public interface coffee {      double getcost(); // returns cost of coffee      string getingredient(); //returns ingredients mixed coffee }  //implementation of simple coffee without ingredients public class simplecoffee : coffee {      double cost;     string ingredient;      public simplecoffee()     {         cost = 1;         ingredient = "coffee";     }      public double getcost()     {         return cost;     }      public string getingredient()     {         return ingredient;     } }    //abstract decorator class - note implements coffee interface abstract public class coffeedecorator : coffee {      protected coffee decoratedcoffee;     protected string ingredientseparator;      public coffeedecorator(coffee decoratedcoffee)     {         this.decoratedcoffee = decoratedcoffee;         ingredientseparator = ", ";     }   public coffeedecorator()  {   }      public double getcost() //note implements getcost function defined in interface coffee     {         return decoratedcoffee.getcost();     }      public string getingredient()     {         return decoratedcoffee.getingredient();     } }  //decorator milk mixes milk coffee //note extends coffeedecorator public class milk : coffeedecorator {      double cost;     string ingredient;      public milk(coffee decoratedcoffee) : base(decoratedcoffee)     {         cost = 0.5;         ingredient = "milk";     }      public double getcost()     {         return base.getcost() + cost;     }      public string getingredient()     {         return base.getingredient() + base.ingredientseparator + ingredient;     } }  //decorator whip mixes whip coffee //note extends coffeedecorator public class whip : coffeedecorator {      double cost;     string ingredient;   public whip(coffee decoratedcoffee)   : base(decoratedcoffee)     {         cost = 0.7;         ingredient = "whip";     }      public double getcost()     {         return base.getcost() + cost;     }      public string getingredient()     {         return base.getingredient() + base.ingredientseparator + ingredient;     } }  //decorator sprinkles mixes sprinkles coffee //note extends coffeedecorator public class sprinkles : coffeedecorator {      double cost;     string ingredient;      public sprinkles(coffee decoratedcoffee) : base(decoratedcoffee)     {          cost = 0.2;         ingredient = "sprinkles";     }      public double getcost()     {   return base.getcost() + cost;     }      public string getingredient()     {   return base.getingredient() + base.ingredientseparator + ingredient;     } }  } 

yes - methods virtual default in java, not in c#.

you should have received warnings when compiling code, talking "new" modifier. should have given clue. milk (etc) methods hiding or shadowing in coffeedecorator - they're not being called polymorphically.

you'd need make coffeedecorator methods virtual virtual modifier, , explicitly override them in milk (etc) override modifier.

// in coffeedecorator public virtual double getcost() {     return decoratedcoffee.getcost(); }  // in milk public override double getcost() {     return base.getcost() + cost; }