享元模式
模式定义
模式动机
- 如果一个应用使用了大量的对象，而大量的对象造成了很大的存储开销时就应该考虑使用
- 当对象的大多数状态为外部状态，如果删除对象的外部状态，那么可以用相对较少的共享内存对象取代很多组对象，此时可以考虑使用享元模式。
UML 类图
优缺点
优点
- 享元模式可以避免大量非常类似的开销。在有些程序中，有时候需要生成大量的细颗粒度的类实例来表示数据，如果他们仅个别参数不同外，就可以使用该模式将不同的参数移到类实例外来，在方法调用的时候将参数传入，这样就可以大幅度地减少单个实例的数目
缺点
- 使用享元模式需要维护一个系统已有的所有享元的列表，而这本身需要耗费资源
- 享元模式使得系统变得更加复杂，为了使对象可以共享，需要将一些状态外部化，这使得程序逻辑复杂化。因此应当在足够多的对象实例可供共享时才值得使用享元模式
源码
/**
* 享元模式：通过共享技术有效地支持大量颗粒细度的对象
*/
#include <string>
#include <iostream>
#include <vector>
using namespace std;
class FlyWeight
{
public:
virtual void Operation(const string& extrinsicState) = 0;
string getIntrinsicState(){
return m_intrinsicState;
}
virtual ~FlyWeight(){}
protected:
FlyWeight(string intrinsicState){
m_intrinsicState = intrinsicState;
}
private:
string m_intrinsicState;
};
class UnsharedConcreteFlyWeight : public FlyWeight
{
public:
virtual void Operation(const string& extrinsicState){
cout << extrinsicState << endl;
}
UnsharedConcreteFlyWeight(string intrinsicState):FlyWeight(intrinsicState){
}
~UnsharedConcreteFlyWeight(){}
private:
};
class ConcreteFlyweight : public FlyWeight
{
public:
virtual void Operation(const string& extrinsicState){
cout << getIntrinsicState() << endl;
cout << extrinsicState << endl;
}
ConcreteFlyweight(string intrisicState):FlyWeight(intrisicState){
}
~ConcreteFlyweight(){}
private:
};
class FlyWeightFactory
{
public:
FlyWeightFactory(){}
~FlyWeightFactory(){}
FlyWeight* getFlyWeight(string key){
vector<FlyWeight*>::iterator it = m_vecPFlyWeight.begin();
for(; it != m_vecPFlyWeight.end(); ++it){
if((*it)->getIntrinsicState() == key){
return *it;
}
}
FlyWeight* p_struFly = new ConcreteFlyweight(key);
m_vecPFlyWeight.push_back(p_struFly);
return p_struFly;
}
void getFlyWeightCount(){
cout << m_vecPFlyWeight.size() << endl;
}
private:
vector<FlyWeight*> m_vecPFlyWeight;
};
class character
{
public:
virtual ~character(){}
virtual void display(int width, int height, int ascent, int descent, int pointSize) = 0;
virtual char getSymbol() = 0;
protected:
char m_symbol;
int m_width;
int m_height;
int m_ascent;
int m_descent;
int m_pointSize;
character(char c){
m_symbol = c;
}
};
class characterA : public character
{
public:
characterA(char c):character(c){}
~characterA(){}
virtual void display(int width, int height, int ascent, int descent, int pointSize){
m_ascent = ascent;
m_height = height;
m_width = width;
m_pointSize = pointSize;
m_descent = descent;
cout << m_symbol << " " << m_ascent << " " << m_descent << " " << m_height << " " << m_pointSize << " " << m_width << endl;
}
virtual char getSymbol(){
return m_symbol;
}
};
#if 0
class characterB : public character
{
public:
characterB(char c):character(c){}
~characterB(){}
virtual void display(int width, int height, int ascent, int descent, int pointSize);
virtual char getSymbol(){
return m_symbol;
}
};
class characterC : public character
{
public:
characterC(char c);
~characterC();
virtual void display(int width, int height, int ascent, int descent, int pointSize);
virtual char getSymbol();
};
class characterD : public character
{
public:
characterD(char c);
~characterD();
virtual void display(int width, int height, int ascent, int descent, int pointSize);
virtual char getSymbol();
};
#endif
class characterFactory
{
public:
characterFactory(){}
~characterFactory(){}
character* getCharacter(char c){
vector<character*>::iterator iter = m_vecCharacter.begin();
for(; iter != m_vecCharacter.end(); ++iter){
if((*iter)->getSymbol() == c) {
return *iter;
}
}
character* p_F = new characterA(c);
m_vecCharacter.push_back(p_F);
return p_F;
}
vector<character*>::size_type getCount(){
return m_vecCharacter.size();
}
private:
vector<character*> m_vecCharacter;
};
int main()
{
#if 0
string extrinsicState = "ext";
FlyWeightFactory* p_struFlyWeightFac = new FlyWeightFactory();
FlyWeight* p_struFlyWeight = p_struFlyWeightFac->getFlyWeight("hello");
// FlyWeight* p_struFlyWeight1 = p_struFlyWeightFac->getFlyWeight("hello");
p_struFlyWeight->Operation(extrinsicState);
p_struFlyWeightFac->getFlyWeightCount();
#endif
int ascent = 70;
int descent = 0;
int height = 100;
int width = 120;
int pointSize = 10;
string test = "AABCDEEFGHO";
string::iterator it = test.begin();
characterFactory* pcF = new characterFactory();
for (; it != test.end(); ++it)
{
pointSize++;
char c = *it;
character* p_charF = pcF->getCharacter(c);
p_charF->display(width,height,ascent,descent,pointSize);
}
vector<character*>::size_type sizeChar = pcF->getCount();
cout << "count: " << sizeChar << endl;
return 0;
}
