装饰者模式——HeaderFirst学习笔记

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1 装饰者模式定义

动态的将责任附加到对象上，想要扩展功能，装饰者提供有别于继承的另外一种选择。

2 装饰者模式精髓

2.1对扩展开放，对修改关闭

2.2继承属于扩展形式之一，但不见得是达到弹性设计的最佳方案

2.3设计应该允许行为被扩展而无需修改现有代码

2.4装饰者意味着一群装饰者类，这些类用来包装具体的组件

2.5装饰者和被装饰者具备同样的类型

2.6装饰者对组件的客户是透明的，除非客户程序依赖组件具体类型

2.7装饰者会产生很多小对象，运用过度会使得程序复杂

3 例子代码

namespace DecoratorDesignPattern{    public interface  Deverage    {         string getDescription();         double cost();    }    public abstract class ConditionDecorator : Deverage    {        public virtual string getDescription()         {             return string.Empty;        }        public virtual double cost()        {            return 0.0;        }    }    public class HouseBlend : Deverage    {        public HouseBlend(string description)        {            m_description = description;        }        private string m_description;        #region Deverage 成员        public string getDescription()        {            return m_description;        }        public double cost()        {            return 100;        }        #endregion    }    public class DarkRoast : Deverage    {        public DarkRoast(string description)        {            m_description = description;        }        private string m_description;        #region Deverage 成员        public string getDescription()        {            return m_description;        }        public double cost()        {            return 200;        }        #endregion    }    public class Decaf : Deverage    {        public Decaf(string description)        {            m_description = description;        }        private string m_description;        #region Deverage 成员        public string getDescription()        {            return "Decaf";        }        public double cost()        {            return 300;        }        #endregion    }    public class Espresso : Deverage    {        public Espresso(string description)        {            m_description = description;        }        private string m_description;        #region Deverage 成员        public string getDescription()        {            return "Espresso";        }        public double cost()        {            return 400;        }        #endregion    }    public class Moca : ConditionDecorator    {        private Deverage m_Deverage;        public Moca(Deverage deverage)        {            m_Deverage = deverage;        }        #region Deverage 成员        public override string getDescription()        {            return m_Deverage.getDescription()+",Moca";        }        public override double cost()        {            return m_Deverage.cost()+20;        }        #endregion    }    public class Soy : ConditionDecorator    {        private Deverage m_Deverage;        public Soy(Deverage deverage)        {            m_Deverage = deverage;        }        #region Deverage 成员        public override string getDescription()        {            return m_Deverage.getDescription() + ",Soy";        }        public override double cost()        {            return m_Deverage.cost() + 30;        }        #endregion    }    public class Whip : ConditionDecorator    {        private Deverage m_Deverage;        public Whip(Deverage deverage)        {            m_Deverage = deverage;        }        #region Deverage 成员        public override string getDescription()        {            return m_Deverage.getDescription() + ",Whip";        }        public override double cost()        {            return m_Deverage.cost() + 40;        }        #endregion    }}namespace DecoratorDesignPattern{    class Program    {        static void Main(string[] args)        {            Deverage pCoffee = new HouseBlend("深焙咖啡");            Deverage pCondiment = new Moca(pCoffee);            pCondiment = new Soy(pCondiment);            pCondiment = new Whip(pCondiment);            Console.WriteLine("咖啡名字为：" + pCondiment.getDescription());            Console.WriteLine("咖啡价格为：" + pCondiment.cost().ToString());        }    }}

4 设计类图

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