装饰者模式

装饰者模式：动态的讲责任附加到对象。若要扩展功能，装饰者提供了比继承更有弹性的替代方案；

关键：装饰者和被装饰着必须是一样的类型，即有共同的超类；利用继承达到类型匹配，而不是获得行为；

原则：对扩展开放，对修改关闭；

缺点：装饰者会导致设计中出现许多小对象，如果过度使用，会让程序变得很复杂；

书中类图框架：

装饰方式：

部分代码：

//装饰者模式#include <iostream>using namespace std;#include <string>class Beverage{string description;public:Beverage():description("Unknown Beverage"){};void set_decrp( const string& str ){description = str;}virtual string getdescription(){return description;}virtual double cost(){return 0.0;}};class Espresso:public Beverage{public:Espresso(){set_decrp( "Espresso");}double cost(){return 1.99;}};class HouseBlend:public Beverage{public:HouseBlend(){set_decrp( "House Blend Coffee");}double cost(){return 0.89;}};class CondimentDecrator:public Beverage{public:virtual string getdescription(){return Beverage::getdescription();}};class Mocha:public CondimentDecrator{Beverage *beverage;public:Mocha(Beverage *beverage){this->beverage = beverage;}string getdescription(){return beverage->getdescription() + " , Mocha";}double cost(){return 0.20 + beverage->cost();}};class Soy:public CondimentDecrator{Beverage *beverage;public:Soy(Beverage *beverage){this->beverage = beverage;}string getdescription(){return beverage->getdescription() + " , Soy";}double cost(){return 0.15 + beverage->cost();}};class Whip:public CondimentDecrator{Beverage *beverage;public:Whip(Beverage *beverage){this->beverage = beverage;}string getdescription(){return beverage->getdescription() + " , Whip";}double cost(){return 0.10 + beverage->cost();}};void test(){Beverage *beverage = new Espresso();beverage = new Mocha( beverage );beverage = new Mocha( beverage );beverage = new Whip( beverage );cout<<beverage->getdescription()<<" $"<<beverage->cost()<<endl;}int main(){<span style="white-space:pre"></span>test();<span style="white-space:pre"></span>return 0;}/**/