装饰者中的一个问题？

Question

我是在HeadFirst上学到的装饰者模式，他是用Java编的，我改成了C#代码，代码如下：
using System;
using System.Collections.Generic;
using System.Text;namespace DesignModel
{
    class DecoratorPattern
    {
        public void TestDecorator()
        {
            Beverage be = new Espresso();
            be = new Mocha(be);
            be = new Mocha(be);
            be = new Whip(be);
            Console.WriteLine(be.getDescription()+" $"+be.cost());
        }
    }//****************************************************
    public abstract class Beverage
    {
       protected string description = "Unknown Beverage";        public string getDescription()
        {
            return description;
        }        public abstract double cost();
    }//++++++++++++++++++++++++++++++++++++++++++++++++++++    public abstract class CondimentDecorator : Beverage
    {
        public abstract string getDescription();
    }//*****************************************************    public class Espresso : Beverage
    {
        public Espresso()
        {
            description = "Espresso";
        }        public override double cost()
        {
            return 1.99;
        }
    }
    public class Mocha : CondimentDecorator
    {
        Beverage beverage;        public Mocha(Beverage beverage)
        {
            this.beverage = beverage;
        }        public override string getDescription()
        {
            return beverage.getDescription() + ", Mocha";
        }        public override double cost()
        {
            return beverage.cost() + 0.20;
        }
    }    public class Whip : CondimentDecorator
    {
        Beverage beverage;        public Whip(Beverage beverage)
        {
            this.beverage = beverage;
        }        public override string getDescription()
        {
            return beverage.getDescription() + ", Whip";
        }        public override double cost()
        {
            return beverage.cost() + 0.70;
        }
    }}
为啥输出的结果是Unknown Beverage
而不是：Espresso, Mocha, Mocha, Whip

Answer 1

 be = new Mocha(be);
 be = new Mocha(be);
 be = new Whip(be);
~~~~~~~~~~~~~~~~~~~~~~~
这边确定没有写错？

Answer 2

你还是自己在好好把装饰者模式看看吧.装饰者的核心是,继承被装饰者类的框架并且添加被装饰者的引用,来增加操作.你建立Beverage 和CondimentDecorator的时候有点问题,粗略把你的程序修改了下.(测试通过)..
using System;
using System.Collections.Generic;
using System.Text;namespace csdn_2009._4._0
{
    class DecoratorPattern
    {
        public void TestDecorator()
        {
            Beverage be = new Espresso();
            be = new Mocha(be);
            be = new Mocha(be);
            be = new Whip(be);
            Console.WriteLine(be.getDescription() + " $" + be.cost());
        }
        static void Main(string[] args)
        {
            DecoratorPattern dp = new DecoratorPattern();
            dp.TestDecorator();
            Console.ReadLine();
        }
    }    //****************************************************
    public abstract class Beverage
    {
        protected string description = "Unknown Beverage";        public abstract string getDescription();
        //{
        //    return description;
        //}        public abstract double cost();
    }    //++++++++++++++++++++++++++++++++++++++++++++++++++++    public abstract class CondimentDecorator : Beverage
    {
        protected Beverage _beverage ;
        //public abstract string getDescription();
    }    //*****************************************************    public class Espresso : CondimentDecorator //Beverage
    {
        public Espresso()
        {
            description = "Espresso";
        }
        public Espresso(Beverage b)
        {
            this._beverage = b;
        }
        public override string  getDescription()
        {
            if (_beverage != null)
                return _beverage.getDescription() + this.description;
            else
                return this.description;
        }        public override double cost()
        {
            if (_beverage != null)
                return _beverage.cost() + 1.99;
            else
                return 1.99;
        }
    }
    public class Mocha : CondimentDecorator
    {
        //Beverage beverage;        public Mocha(Beverage beverage)
        {
            this._beverage = beverage;
        }        public override string getDescription()
        {
            if (_beverage != null)
                return _beverage.getDescription() + ", Mocha";
            else
                return "Mocha";
        }        public override double cost()
        {
            if (_beverage != null)                return _beverage.cost() + 0.20;
            else
                return 0.20;
        }
    }    public class Whip : CondimentDecorator
    {
        //Beverage beverage;        public Whip(Beverage beverage)
        {
            this._beverage = beverage;
        }        public override string getDescription()
        {
            if (_beverage != null)
                return _beverage.getDescription() + ", Whip";
            else
                return "Whip";
        }        public override double cost()
        {
            if (_beverage != null)
                return _beverage.cost() + 0.70;
            else
                return 0.70;
        }
    }
}

Answer 3

整理了下,希望能对你有帮助.个人认为如下写比较规范清晰明了.
using System;
using System.Collections.Generic;
using System.Text;namespace _009._4._0
{
    class Program
    {
        static void Main(string[] args)
        {
            Espresso espresso = new Espresso();
            CondimentDecorator decorator1 = new MochaDecorator(espresso);
            CondimentDecorator decorator2 = new MochaDecorator(decorator1);
            CondimentDecorator decorator3 = new WhipDecorator(decorator2);
            CondimentDecorator decorator4 = new EspressoDecorator(decorator3);
            Console.WriteLine(decorator4.getDescription() + "\tCost :" + decorator4.cost());
            Console.ReadLine();
        }
    }
    public abstract class Beverage
    {
        protected string description = "Unknown Beverage";        public abstract string getDescription();
       
        public abstract double cost();
    }    public abstract class CondimentDecorator : Beverage
    {
        protected Beverage _beverage;       
    }    public class Espresso : Beverage
    {
        public Espresso()
        {
            description = "Espresso";
        }        
        public override string getDescription()
        {            
                return this.description;
        }        public override double cost()
        {            
                return 1.99;
        }
    }
    public class Mocha : Beverage
    {
        public Mocha()
        {
            description = "Mocha";
        }
        public override string getDescription()
        {
            return this.description;
        }        public override double cost()
        {
            return 0.20;
        }
    }
    public class Whip : Beverage
    {
        public Whip()
        {
            description = "Whip";
        }
        public override string getDescription()
        {
            return this.description;
        }        public override double cost()
        {
            return 0.70;
        }
    }    public class MochaDecorator : CondimentDecorator
    {
       
        public MochaDecorator(Beverage beverage)
        {
            this._beverage = beverage;
        }        public override string getDescription()
        {            
                return _beverage.getDescription() + ", Mocha";
            
        }        public override double cost()
        {           
                return _beverage.cost() + 0.20;
          
        }
    }
    public class WhipDecorator : CondimentDecorator
    {
        
        public WhipDecorator(Beverage beverage)
        {
            this._beverage = beverage;
        }        public override string getDescription()
        {
            return _beverage.getDescription() + ", Whip";        }        public override double cost()
        {
            return _beverage.cost() + 0.70;        }
    }
    public class EspressoDecorator : CondimentDecorator
    {
        public EspressoDecorator(Beverage beverage)
        {
            this._beverage = beverage;
        }        public override string getDescription()
        {
            return _beverage.getDescription() + ", Espresso";        }        public override double cost()
        {
            return _beverage.cost() + 1.99;        }
    }}