装饰者模式Decorator – 学习HeadFirst设计模式记录

 

装饰者模式：

     动态的将责任附加到对象上。若要扩展功能，装饰者提供了比继承更有弹性的替代方案。

 

     装饰者和被装饰者有相同的超类型。

     装饰者可以在所委托被装饰者的行为之前或之后，加上自己的行为，以达到特定的目的。

 

     OO原则：多用组合，少用继承。

  

1、装饰者和被装饰者共同的基类

/*Beverage饮料*/
class Beverage 
{
public:
    Beverage()
    {
        _description = "Unknow Beverage";
    }

    virtual std::string GetDescription()
    {
        return _description;
    }
    virtual double Cost() = 0;
    
protected:
    std::string _description;
};

2、被装饰者类

/*Espresso浓咖啡*/
class Espresso : public Beverage
{
public:
    Espresso()
    {
        _description = "Espresso Coffee";
    }

    virtual double Cost()
    {
        return 1.99;
    }
};

/*HouseBlend综合咖啡,星巴克独家调配咖啡*/
class HouseBlend : public Beverage
{
public:
    HouseBlend()
    {
        _description = "House Blend Coffee";
    }
    
    virtual double Cost()
    {
        return 1.99;
    }
};

 

3、装饰者类

  
/*Condiment调味品*/
class CondimentDecorator : public Beverage
{
public:
    CondimentDecorator()
    {
        _description = "Condiment Decorator";
    }
    
    virtual double Cost() = 0;
};

/*Mocha调味品摩卡*/
class Mocha : public CondimentDecorator
{
public:
    Mocha(Beverage *beverage)
    {
        _beverage = beverage;
        _description = beverage->GetDescription();
        _description += " + Mocha";
    }

    virtual double Cost()
    {
        return 0.2 + _beverage->Cost();
    }

private:
    Beverage *_beverage;
};

/*Whip调味品奶泡*/
class Whip : public CondimentDecorator
{
public:
    Whip(Beverage *beverage)
    {
        _beverage = beverage;
        _description = beverage->GetDescription();
        _description += " + Whip";
    }
    
    virtual double Cost()
    {
        return 0.2 + _beverage->Cost();
    }
    
private:
    Beverage *_beverage;
};

/*Soy调味品豆浆*/

class Soy : public CondimentDecorator

{

public:

  Soy(Beverage *beverage)

    {

  _beverage = beverage;

  _description = beverage->GetDescription();

  _description += " + Sop";

  }

  virtual double Cost()

  {

  return 0.2 + _beverage->Cost();

  }

private:

  Beverage *_beverage;

};

 4、测试代码

int main()
{
    std::cout<<"Decorator patten."<<std::endl<<std::endl; 

    Beverage *beverage = new Espresso();  /*未添加装饰*/
    std::cout<<beverage->GetDescription().c_str()<<" , $"<<beverage->Cost()<<std::endl;

    Beverage *beverage2 = new HouseBlend();
    beverage2 = new Mocha(beverage2);  /*添加装饰*/
    beverage2 = new Mocha(beverage2);  /*添加装饰*/
    beverage2 = new Whip(beverage2);   /*添加装饰*/

    beverage2 = new Soy(beverage2);    /*添加装饰*/

    std::cout<<beverage2->GetDescription().c_str()<<" , $"<<beverage2->Cost()<<std::endl;

    return 0;
}