目录
C++设计模式-享元（Flyweight）
一、意图
二、适用性
三、结构
四、参与者
五、代码
C++设计模式-享元（Flyweight）
一、意图
运用共享技术有效地支持大量细粒度的对象。
二、适用性
- 一个应用程序使用了大量的对象。
- 完全由于使用大量的对象，造成很大的存储开销。
- 对象的大多数状态都可变为外部状态。
- 如果删除对象的外部状态，那么可以用相对较少的共享对象取代很多组对象。
- 应用程序不依赖于对象标识。由于Flyweight对象可以被共享，对于概念上明显有别的对象，标识测试将返回真值。
三、结构
四、参与者
- Flyweight
描述一个接口，通过这个接口flyweight可以接受并作用于外部状态。
- ConcreteFlyweight
实现Flyweight接口，并为内部状态（如果有的话）增加存储空间。ConcreteFlyweight对象必须是可共享的。它所存储的状态必须是内部的；即，它必须独立于ConcreteFlyweight对象的场景。
- UnsharedConcreteFlyweight
并非所有的Flyweight子类都需要被共享。Flyweight接口使共享成为可能，但它并不强制共享。在Flyweight对象结构的某些层次，UnsharedConcreteFlyweight对象通常将ConcreteFlyweight对象作为子节点。
-
FlyweightFactory
创建并管理flyweight对象。
确保合理地共享flyweight。当用户请求一个flyweight时，FlyweightFactory对象提供一个已创建的实例或者创建一个（如果不存在的话）。
-
Client
维持一个对flyweight的引用。
计算或存储一个（多个）flyweight的外部状态。
五、代码
#include<iostream>
#include<vector>
using namespace std;
class Flyweight {
public:
Flyweight(string tempIntrinsicState) {
this->intrinsicState = tempIntrinsicState;
}
string GetIntrinsicState() {
return intrinsicState;
}
virtual void Operation(const string& tempExtrinsicState) = 0;
private:
string intrinsicState;
};
class ConcreteFlyweight :public Flyweight {
public:
ConcreteFlyweight(string tempIntrinsicState) :Flyweight(tempIntrinsicState) {}
void Operation(const string& tempExtrinsicState) {
cout << this->GetIntrinsicState() << endl;
cout << tempExtrinsicState << endl;
}
};
class UnsharedConcreteFlyweight : public Flyweight {
public:
UnsharedConcreteFlyweight(string tempIntrinsicState) :Flyweight(tempIntrinsicState) {}
void UnsharedConcreteOperation(const string& tempExtrinsicState) {
cout << tempExtrinsicState << endl;
}
};
class FlyweightFactory {
public:
Flyweight* GetFlyweight(string state) {
vector<Flyweight*>::iterator it = this->flyweightVector.begin();
for (; it != this->flyweightVector.end(); it++) {
if ((*it)->GetIntrinsicState() == state) {
return *it;
}
}
Flyweight* flyweight = new ConcreteFlyweight(state);
this->flyweightVector.push_back(flyweight);
return flyweight;
}
int GetFlyweightCount() {
return this->flyweightVector.size();
}
private:
vector<Flyweight*> flyweightVector;
};
int main() {
string extrinsicState = "ExtrinsicState";
FlyweightFactory* flyweightFactory = new FlyweightFactory();
Flyweight* flyweight1 = flyweightFactory->GetFlyweight("AAA");
Flyweight* flyweight2 = flyweightFactory->GetFlyweight("AAA");
Flyweight* flyweight3 = flyweightFactory->GetFlyweight("BBB");
flyweight1->Operation(extrinsicState);
cout << flyweightFactory->GetFlyweightCount() << endl;
cout << (flyweight1 == flyweight2) << endl;
return 0;
}
