裝飾者模式C#（head first設計模式）

  /// <summary>
    /// 飲料抽象類
    /// </summary>
    public abstract class Beverage
    {
        protected string description = "Unknown Beverage!";

        public string getDescription()
        {
            return description;
        }

        public abstract double cost();
    }


    /// <summary>
    /// 調料抽象類
    /// </summary>
    public abstract class CondimentDecorator : Beverage
    {
        public new abstract string getDescription();
    }


    /// <summary>
    /// 濃縮咖啡
    /// </summary>
    public class Espresso : Beverage
    {
        public Espresso()
        {
            description = "Espresso";
        }

        public override double cost()
        {
            return 1.99;
        }
    }


    public class HouseBlend : Beverage
    {
        public HouseBlend()
        {
            description = "HouseBlend";
        }

        public override double cost()
        {
            return 0.89;
        }
    }

    public class Mocha:CondimentDecorator
    {
        Beverage beverage;
        public Mocha(Beverage b)
        {
            this.beverage = b;
        }

        public override string getDescription()
        {
            return beverage.getDescription() + ",Mocha";
        }

        public override double cost()
        {
            return 0.2 + beverage.cost();
        }
    }

    public class Soy : CondimentDecorator
    {
        Beverage beverage;
        public Soy(Beverage b)
        {
            this.beverage = b;
        }

        public override string getDescription()
        {
            return beverage.getDescription() + ",Soy";
        }

        public override double cost()
        {
            return 0.8 + beverage.cost();
        }
    }

    public class Whip : CondimentDecorator
    {
        Beverage beverage;
        public Whip(Beverage b)
        {
            this.beverage = b;
        }

        public override string getDescription()
        {
            return beverage.getDescription() + ",Whip";
        }

        public override double cost()
        {
            return 1.8 + beverage.cost();
        }
    }

    public void main(){
        //濃縮咖啡 不加調料
        Beverage beverage = new Espresso();
        Debug.WriteLine(beverage.getDescription() + ":" + beverage.cost().ToString());

        Beverage beverage2 = new HouseBlend();
        beverage2 = new Soy(beverage2);
        beverage2 = new Mocha(beverage2);
        beverage2 = new Whip(beverage2);
        Debug.WriteLine(beverage2.getDescription() + ":" + beverage2.cost().ToString());
    }

開放-關閉原則：類應該對擴展開放，對修改關閉；

裝飾者模式：動態的將責任附加到對象上。想要擴展功能，裝飾者提供有別於繼承的另外一種選擇；