[GoF设计模式]Flyweight模式和State模式的C++实现

【Flyweight模式】

 一个应用程序创建了太多的对象，会造成很大的存储开销，特别是大量轻量级的对象。对于这种情况，可以将对象的状态分成外部状态和内部状态，将可以被共享(不变化)的状态作为内部状态存储在对象中，而外部状态则可以将外部对象作为参数传递给对象。Flyweight有一个类似工厂模式的对象构造工厂，当程序需要一个对象时就会向FlyweightFactory发出请求对象的消息，该工厂拥有一个管理、存储对象的仓库（或者称为对象池），FlyweightFactory中会遍历对象池，如果存在则直接返回，否则创建并返回。同时程序也可以向FlyweightFactory请求不被共享的对象。

【图解】

以纯文本为例，每个字符CharFlyweight为共享的轻量级对象，而由这些字符构成的行则为非共享的对象RowFlyweight，而TextFlyweightFactory则管理其共享对象的对象池。当用户向该工厂请求字符时，就从对象池中取得，而当用户向该工厂请求字符串时候则通过创建非共享的RowFlyweight获取，但此种每个字符的获取仍然向TextFlyweightFactory共享对象的对象池提出请求。

 

【程序】

 /********************************************************************* DESCRIPTION:Text Flyweight Factory Class** AUTHOR:Neesky** DATE:2009-10-4********************************************************************/#ifndef TEXTFLYWEIGHTFACTORY_H_#define TEXTFLYWEIGHTFACTORY_H_/** include files **/#include <vector>#include "CharFlyweight.h"using namespace std;/** * TextFlyweightFactory: provide the CharFlyweight object * * @author roy nee (2009-10-4) */class TextFlyweightFactory{public: /*Constructor and destructor*/ TextFlyweightFactory(){} virtual ~TextFlyweightFactory(){} /// <summary> /// Get the CharFlyweight Object /// </summary> /// <param name="_char"></param> /// <returns></returns> virtual AbstractFlyweight* GetFlyweight(char _char) { vector<CharFlyweight*>::iterator iter=this->_vecCharFlyweight.begin(); for(;iter!=this->_vecCharFlyweight.end();++iter) { if((*iter)->GetChar()==_char)return *iter; } CharFlyweight *newchar=new CharFlyweight(_char);/*new character*/ this->_vecCharFlyweight.push_back(newchar); /*Record it*/ return newchar; } virtual AbstractFlyweight* GetFlyweight(string str) { RowFlyweight *row=new RowFlyweight(); for(int i=0;i<str.length();++i) row->AddFlyweight(this->GetFlyweight(str[i])); /*Get the char from VecCharFlyweight*/ return row; } /// <summary> /// Just be used to show the size of vector /// </summary> /// <returns></returns> virtual int SizeVector() { return this->_vecCharFlyweight.size(); }private: /*CharFlyweight Vector*/ vector<CharFlyweight*> _vecCharFlyweight;};#endif 

/********************************************************************* DESCRIPTION: AbstractFlyweight Class [Abstract Class Of Flyweight]** AUTHOR:Neesky** DATE:2009-10-4********************************************************************/#ifndef ABSTRACTFLYWEIGHT_H_#define ABSTRACTFLYWEIGHT_H_/** include files **/#include <iostream>using namespace std;/** * AbstractFlyweight Class[Abstract Class] * * @author roy nee (2009-10-4) */class AbstractFlyweight{public: AbstractFlyweight(){} virtual ~AbstractFlyweight(){} /// <summary> /// Interface of Writing the Element of Flyweight /// </summary> /// <returns></returns> virtual void Write()=0;};#endif 

/********************************************************************* DESCRIPTION: Char Flyweight Class [Concrete Flyweight Class]* SharedFlyweight Class* AUTHOR:Neesky** DATE:2009-10-4********************************************************************/#ifndef CHARFLYWEIGHT_H_#define CHARFLYWEIGHT_H_/** include files **/#include "AbstractFlyweight.h"class CharFlyweight:public AbstractFlyweight{public: /*constructor and destructor*/ CharFlyweight(char tChar) { this->_Char=tChar; } virtual ~CharFlyweight(){} /// <summary> /// Interface of Writing the Element of Flyweight /// </summary> /// <returns></returns> virtual void Write() { cout<<this->_Char<<flush; return; } /// <summary> /// Get the Char /// </summary> /// <returns></returns> virtual char GetChar() { return this->_Char; }private: char _Char;};#endif 

/********************************************************************* DESCRIPTION:Row Flyweight Class [Unshared Flyweight Class]** AUTHOR:Neesky** DATE:2009-10-4********************************************************************/#ifndef ROWFLYWEIGHT_H_#define ROWFLYWEIGHT_H_/** include files **/#include <vector>#include "AbstractFlyweight.h"using namespace std;class RowFlyweight:public AbstractFlyweight{public: RowFlyweight(){} virtual ~RowFlyweight(){} /// <summary> /// Interface of Writing the Element of Flyweight /// </summary> /// <returns></returns> virtual void Write() { for(vector<AbstractFlyweight*>::iterator iter=this->_vecFlyweight.begin();iter!=this->_vecFlyweight.end();++iter) (*iter)->Write(); return; } virtual void AddFlyweight(AbstractFlyweight * flyweight) { this->_vecFlyweight.push_back(flyweight); }private: vector<AbstractFlyweight*> _vecFlyweight;};#endif 

/********************************************************************* DESCRIPTION:Flyweight Pattern [享元模式]** AUTHOR:Neesky** DATE:2009-10-4********************************************************************//** include files **/#include <iostream>#include "CharFlyweight.h"#include "RowFlyweight.h"#include "TextFlyweightFactory.h"using namespace std;int main (int argc, char *argv[]){ /*Now There is A factory*/ TextFlyweightFactory *factory=new TextFlyweightFactory(); /*Now Get CharFlyweight-shared*/ factory->GetFlyweight('a')->Write(); factory->GetFlyweight('a')->Write(); factory->GetFlyweight('c')->Write(); cout<<"/nFactory's Size is: "<<factory->SizeVector()<<endl; /*Now New a Row-unshared*/ factory->GetFlyweight("hello")->Write(); return(0);} 

【输出】

 

 

【State模式】

允许一个对象在其内部状态改变时改变它的行为。对象看起来似乎修改了它的类。FSM有限状态自动机也是一个典型的状态模式，对输入有同的相应(状态转移)，通常情况会写很多switch case 或者 if else语句，当状态数目很多时，维护一组swith case 很困难，状态逻辑和动作没能实现分开，在系统实现中，动作的实现代码直接写在状态逻辑中，使得系统的扩展性和维护性得不到保证。state模式也有问题是，状态逻辑分散到了很多state子类中，很难看到整个逻辑状态图，代码的维护难度也会加大。一般而言状态采用单例模式。注意单例模式中cpp文件中现代码，单例的初始化 GreenState* GreenState::_instance=0;必须在cpp文件中，在h文件中直接初始化或者不写编译会出问题。

【图解】

以交通灯的红灯和绿灯状态为例子(简单起见省略黄灯状态)，交通灯(Context),红灯/绿灯状态(Concrete State，状态采用单例模式)

 

【程序】

/********************************************************************* DESCRIPTION:Traffic Light Class [Context Class]** AUTHOR:Neesky** DATE:2009-10-4********************************************************************/#ifndef TRAFFICLIGHT_H_#define TRAFFICLIGHT_H_/** include files **/#include "TrafficLightState.h"class TrafficLightState;/*predeclaration*//** * Traffic Light Class * * @author roy nee (2009-10-4) */class TrafficLight{public: TrafficLight(TrafficLightState *state); virtual ~TrafficLight(); /// <summary> /// Change the State of Traffic Light /// </summary> /// <param name="state"></param> /// <returns></returns> virtual void ChangeState(TrafficLightState *state); /// <summary> /// Just See the State of TrafficLight /// </summary> /// <returns></returns> virtual void ShowState();private: TrafficLightState *_state;};#endif 

/********************************************************************* DESCRIPTION:** AUTHOR:** DATE:2009-10-4********************************************************************//** include files **/#include "TrafficLight.h"TrafficLight::TrafficLight(TrafficLightState *state){ this->_state=state;}TrafficLight::~TrafficLight(){}void TrafficLight::ChangeState(TrafficLightState *state){ this->_state=state;/*set the state*/ return;}void TrafficLight::ShowState(){ this->_state->ShowState(); return;} 

/********************************************************************* DESCRIPTION:Traffic Light State [Abstract State Class]** AUTHOR:Neesky** DATE:2009-10-4********************************************************************/#ifndef TRAFFICLIGHTSTATE_H_#define TRAFFICLIGHTSTATE_H_/** include files **/#include <iostream>#include "TrafficLight.h"using namespace std;class TrafficLight;/*Predeclaration*//** * TrafficLight State * * @author roy nee (2009-10-4) */class TrafficLightState{public: virtual ~TrafficLightState(); virtual void SetTrafficLight(TrafficLight *trafficlight)=0; virtual void ShowState()=0;protected:/*Singleton Pattern: constructor should be protected or private*/ TrafficLightState();};#endif 

 

/********************************************************************* DESCRIPTION: TrafficLightState CPP File** AUTHOR:** DATE:2009-10-4********************************************************************//** include files **/#include "TrafficLightState.h"TrafficLightState::TrafficLightState(){}TrafficLightState::~TrafficLightState(){} 

 

RedState和GreenState类似，省略.....

/********************************************************************* DESCRIPTION:Green State Class [Concrete State Class]** AUTHOR:Neesky** DATE:2009-10-4********************************************************************/#ifndef GREENSTATE_H_#define GREENSTATE_H_/** include files **/#include "TrafficLightState.h"/** * Green State Class : Concrete State * * @author roy nee (2009-10-4) */class GreenState:public TrafficLightState{public: /*Singleton Pattern's interface to get object instance*/ static GreenState* Instance() { if(_instance==0)_instance=new GreenState(); return _instance; } virtual ~GreenState(); virtual void SetTrafficLight(TrafficLight *trafficlight); virtual void ShowState();protected: GreenState();/*Singleton Pattern: private or pretected*/private: static GreenState* _instance;};#endif 

/********************************************************************* DESCRIPTION: GreenState cpp** AUTHOR:Neesky** DATE:2009-10-4********************************************************************//** include files **/#include "GreenState.h"/*Very Important for Singleton Pattern, it must be written in cpp file*/GreenState* GreenState::_instance=0;GreenState::GreenState(){ }GreenState::~GreenState(){}void GreenState::SetTrafficLight(TrafficLight *trafficlight){ trafficlight->ChangeState(this);}void GreenState::ShowState(){ cout<<"Traffic Light: Green......"<<endl; return;} 

 

【输出】