装饰模式问题

Question

public abstract class Beverage
    {
        public string description;
        public string getDescription()
        {
            return description;
        }
        public abstract double cost();
    }
public abstract class CondimentDecorator:Beverage
    {
        public abstract string getDescription();
    }
public class DarkRoast:Beverage
    {
        public DarkRoast()
        {
            description = "DarkRoast";
        }
        public override double cost()
        {
            return 2.0;
        }
    }
public class Milk:CondimentDecorator
    {
        private Beverage beverage;
        public Milk(Beverage beverage)
        {
            this.beverage = beverage;
        }
        public override string getDescription()
        {
            return beverage.getDescription() + ",Milk";
        }
        public override double cost()
        {
            return beverage.cost() + 0.3;
        }
    }
 public class Mocha:CondimentDecorator
    {
        private Beverage beverage;
        public Mocha(Beverage beverage)
        {
            this.beverage = beverage;
        }
        public override string getDescription()
        {
            return beverage.getDescription() + ",Mocha";
        }
        public override double cost()
        {
            return beverage.cost() + 0.2;
        }
    }
class Program
    {
        static void Main(string[] args)
        {            
            Beverage beverage = new DarkRoast();
            Mocha mocha=new Mocha(beverage);
            Milk milk=new Milk(mocha);
            Console.WriteLine(milk.getDescription() + "$" + milk.cost());
            Console.ReadKey();
        }
    }
正确的结果应该为DarkRoast,Milk,Mocha $2.5大神求助装饰模式

Answer 1

    public abstract class Beverage
    {
        public string description;
        public virtual string getDescription()
        {
            return description;
        }
        public abstract double cost();
    }
    public class DarkRoast : Beverage
    {
        public DarkRoast()
        {
            description = "DarkRoast";
        }
        public override double cost()
        {
            return 2.0;
        }
    }
    public class Milk : Beverage
    {
        private Beverage beverage;
        public Milk(Beverage beverage)
        {
            this.beverage = beverage;
        }
        public override string getDescription()
        {
            return beverage.getDescription() + ",Milk";
        }
        public override double cost()
        {
            return beverage.cost() + 0.3;
        }
    }
    public class Mocha : Beverage
    {
        private Beverage beverage;
        public Mocha(Beverage beverage)
        {
            this.beverage = beverage;
        }
        public override string getDescription()
        {
            return beverage.getDescription() + ",Mocha";
        }
        public override double cost()
        {
            return beverage.cost() + 0.2;
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Beverage beverage = new DarkRoast();
            Mocha mocha = new Mocha(beverage);
            Milk milk = new Milk(mocha);
            Console.WriteLine(milk.getDescription() + "$" + milk.cost());
            Console.ReadKey();
        }    }
这样就行了呀为什么要加一个抽象方法
     public abstract class CondimentDecorator:Beverage
    {
        public abstract string getDescription();
    }