结构型模式之装饰模式(Decorator Pattern)C++实现

装饰模式(Decorator Pattern)结构型模式.

设计原则:类应该对扩展开放,对修改关闭.

例子:用调料来装饰饮料。比如说顾客想要摩卡和奶泡深焙咖啡，那么要做的是：

1.拿一个深焙咖啡(DarkRoast)对象

2.以摩卡(Mocha)对象去装饰它

3.以奶泡(Whip)对象去装饰它

4.调用cost()方法，并依赖委托(delegate)将调料的价格加上去。

装饰着和被装饰者对象有相同的超类型(关键)。通过继承达到类型匹配而不是获取行为。可以用一个或多个装饰者包装一个对象。

定义：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。

HeadFirst中咖啡店的类图如下：

C++实现代码如下：

Component.h头文件：

#ifndef _COMPONENT_H_#define _COMPONENT_H_#include <string>using namespace std;//饮料抽象类class Beverage{public:virtual string getDescription();virtual double cost()=0;protected:string description;};//抽象装饰者调料类class CondimentDecorator:public Beverage{public:virtual string getDescription()=0;};//具体饮料，被装饰的对象class Espresso:public Beverage{public:Espresso();~Espresso();double cost();};class HouseBlend:public Beverage{public:HouseBlend();~HouseBlend();double cost();};//具体调料类class Mocha:public CondimentDecorator{public:Mocha(Beverage *beverage);string getDescription();double cost();private:Beverage *beverage; //记录被装饰者，即饮料};#endif

Component.CPP源文件

#include "Component.h"#include <iostream>#include <string>using namespace std;string Beverage::getDescription(){return description;}//被装饰者类HouseBlend::HouseBlend(){description="House Blend Coffee";}HouseBlend::~HouseBlend(){cout<<"~HouseBlend()"<<endl;}double HouseBlend::cost(){return 0.89;}Espresso::Espresso(){description="Espresso";}Espresso::~Espresso(){cout<<"~Espresso()"<<endl;}double Espresso::cost(){return 1.99;}//装饰者类Mocha::Mocha(Beverage *beverage){this->beverage=beverage;}string Mocha::getDescription(){return beverage->getDescription()+",Mocha";}double Mocha::cost(){return 0.20+beverage->cost();}

主函数main.CPP

#include "Component.h"#include <iostream>using namespace std;int main(int argc,char* argv[]){  //订一杯Espresso，不需要调料，并打印出描述及其价格  Beverage *beverage=new Espresso();  cout<<beverage->getDescription()<<" $"<<beverage->cost()<<endl; //订一杯HouseBlend并加入Mocha调料，打印出描述及其价格  Beverage *beverage2=new HouseBlend();  beverage2=new Mocha(beverage2); //用Mocha去装饰HouseBlend  cout<<beverage2->getDescription()<<" $"<<beverage2->cost()<<endl;return 0;}