我正在阅读关于创建设计模式的文章,并设法完全混淆了工厂,抽象工厂和工厂方法。
我在下面发布了一个代码片段。有人会好心让我知道哪一个是这和(如果可能的话)可以对代码做什么改变,使其属于其他类别?
#include "iostream.h"
#define QUIT 2
class Shape {
public:
virtual void draw() = 0;
};
class Circle : public Shape {
public:
void draw() {
cout << "circle : draw" << endl;
}
};
class Square : public Shape {
public:
void draw() {
cout << "square : draw" << endl;
}
};
class Factory {
public:
virtual Shape* createInstance(int id) = 0;
};
class SimpleShapeFactory : public Factory {
public:
Shape* createInstance( int id) {
if(id == 0)
return new Circle;
else if(id == 1)
return new Square;
else
return new Circle; //as a default
}
};
int main() {
Factory* factory = new SimpleShapeFactory();
int choice = 0;
Shape* shape;
do
{
cout<<"n 0. Circle";
cout<<"n 1. Square";
cout<<"n 2. Quit";
cout<<"n Enter your choice : ";
cin>>choice;
if(choice == QUIT)
break;
shape = factory->createInstance(choice);
shape->draw();
} while (choice !=QUIT);
}
这不是GOF的创建模式。它是抽象工厂模式的一种变体,有时称为参数化工厂模式。参数化工厂根据传递给create方法的参数(通常是Id或类型说明符)创建不同的对象。
示例中的GOF工厂方法是这样的(只是一个示例…非意义…)
struct AreaCalculator {
virtual double calculateArea() = 0;
};
struct CircleCalculator {
CircleCalculator(const Circle& circle);
double calculateArea() override;
};
struct Shape {
virtual void draw() = 0;
// This is the factory method:
virtual std::unique_ptr<AreaCalculator> createCalculator() = 0;
};
struct Circle : Shape {
void draw() override {
cout << "circle : draw" << endl;
}
std::unique_ptr<AreaCalculator> createCalculator() {
return make_unique<AreaCalculator>(*this);
}
};
一个GOF抽象工厂应该是这样的
struct Circle {
virtual void draw() = 0;
};
struct StdoutCircle : Circle {
void draw() override {
cout << "circle : draw" << endl;
}
};
struct Win32Circle : Circle {
void draw() override {
// ....
}
};
struct ShapeFactory {
virtual std::unique_ptr<Circle> createCircle() = 0;
virtual std::unique_ptr<Rect> createRect() = 0;
};
struct StdoutShapeFactory : ShapeFactory {
std::unique_ptr<Circle> createCircle() override {
return make_unique<StdoutCircle>();
}
std::unique_ptr<Rect> createRect() override {
// ...
}
};
有两种相关的模式:工厂方法模式和抽象工厂模式。你的接近第二个。有No模式命名为Abstract。