设计模式(3)-工厂模式
工厂模式是什么？
工厂模式又称为虚拟构造子模式或多态工厂模式，是在简单工厂模式的基础上，将核心角色“工厂类”改为层次继承结构，提取出一个抽象工厂的角色，由对应具体产品的具体工厂类来继承此抽象工厂，并提供抽象工厂的多态性，对外提供统一的产品创建接口。
工厂模式示意图如下所示。可以看出，创建产品的职责不再和简单工厂模式那样，集中在单个工厂类，而是分散到各具体工厂类，这样，既继承了简单工厂模式的优点：由工厂类承担创建产品的责任，客户类只需“消费”产品；又避免了其单个工厂类责任过于集中，新增产品需修改工厂类源代码的缺点。
工厂模式示例：水果农场
#include <iostream>
#include <string>
#include <algorithm>
class Fruit {
public:
virtual void grow() = 0;
virtual void plant() = 0;
virtual void harvest() = 0;
};
class Apple : public Fruit {
public:
void grow() override
{
std::cout << "grow apple" << std::endl;
}
void plant() override
{
std::cout << "plant apple" << std::endl;
}
void harvest() override
{
std::cout << "harvest apple" << std::endl;
}
void SetTreeAge(uint32_t treeAge) { treeAge_ = treeAge; }
uint32_t GetTreeAge() const { return treeAge_; }
private:
uint32_t treeAge_ = 0;
};
class Grape : public Fruit {
public:
void grow() override
{
std::cout << "grow grape" << std::endl;
}
void plant() override
{
std::cout << "plant grape" << std::endl;
}
void harvest() override
{
std::cout << "harvest grape" << std::endl;
}
void SetSeedless(bool seedless) { seedless_ = seedless; }
bool IsSeedledd() const { return seedless_; }
private:
bool seedless_ = false;
};
class FruitGardener {
public:
virtual Fruit *Factory() = 0;
};
class AppleGardener: public FruitGardener {
public:
Fruit * Factory() override
{
return new Apple();
}
};
class GrapeGardener: public FruitGardener {
public:
Fruit * Factory() override
{
return new Grape();
}
};
int main()
{
std::cout << "=== create apple ===" << std::endl;
FruitGardener *appleGardener = new AppleGardener();
auto *apple = appleGardener->Factory();
apple->grow();
apple->harvest();
apple->plant();
std::cout << "=== create grape ===" << std::endl;
FruitGardener *grapeGardener = new GrapeGardener();
auto *grape = grapeGardener->Factory();
grape->grow();
grape->harvest();
grape->plant();
delete apple;
delete grape;
delete appleGardener;
delete grapeGardener;
}
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参考
《Java与模式》第13章
