强调工厂方法的理由是
可以使不同类型的工厂派生自基本类型的工厂
工厂方法模式事实上是多态工厂模式的一个特例
//: C10:ShapeFactory2.cpp
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// Polymorphic Factory Methods.
#include <iostream>
#include <map>
#include <string>
#include <vector>
#include <stdexcept>
#include <cstddef>
#include "../purge.h"
using namespace std;
class Shape {
public:
virtual void draw() = 0;
virtual void erase() = 0;
virtual ~Shape() {}
};
class ShapeFactory {
virtual Shape* create() = 0;
static map<string, ShapeFactory*> factories;
public:
virtual ~ShapeFactory() {}
friend class ShapeFactoryInitializer;
class BadShapeCreation : public logic_error {
public:
BadShapeCreation(string type)
: logic_error("Cannot create type " + type) {}
};
static Shape*
createShape(const string& id) throw(BadShapeCreation) {
if(factories.find(id) != factories.end())
return factories[id]->create();
else
throw BadShapeCreation(id);
}
};
// Define the static object:
map<string, ShapeFactory*> ShapeFactory::factories;
class Circle : public Shape {
Circle() {} // Private constructor
friend class ShapeFactoryInitializer;
class Factory;
friend class Factory;
class Factory : public ShapeFactory {
public:
Shape* create() { return new Circle; }
friend class ShapeFactoryInitializer;
};
public:
void draw() { cout << "Circle::draw" << endl; }
void erase() { cout << "Circle::erase" << endl; }
~Circle() { cout << "Circle::~Circle" << endl; }
};
class Square : public Shape {
Square() {}
friend class ShapeFactoryInitializer;
class Factory;
friend class Factory;
class Factory : public ShapeFactory {
public:
Shape* create() { return new Square; }
friend class ShapeFactoryInitializer;
};
public:
void draw() { cout << "Square::draw" << endl; }
void erase() { cout << "Square::erase" << endl; }
~Square() { cout << "Square::~Square" << endl; }
};
// Singleton to initialize the ShapeFactory:
class ShapeFactoryInitializer {
static ShapeFactoryInitializer si;
ShapeFactoryInitializer() {
ShapeFactory::factories["Circle"]= new Circle::Factory;
ShapeFactory::factories["Square"]= new Square::Factory;
}
~ShapeFactoryInitializer() {
map<string, ShapeFactory*>::iterator it =
ShapeFactory::factories.begin();
while(it != ShapeFactory::factories.end())
delete it++->second;
}
};
// Static member definition:
ShapeFactoryInitializer ShapeFactoryInitializer::si;
char* sl[] = { "Circle", "Square", "Square",
"Circle", "Circle", "Circle", "Square" };
int main() {
vector<Shape*> shapes;
try {
for(size_t i = 0; i < sizeof sl / sizeof sl[0]; i++)
shapes.push_back(ShapeFactory::createShape(sl[i]));
} catch(ShapeFactory::BadShapeCreation e) {
cout << e.what() << endl;
return EXIT_FAILURE;
}
for(size_t i = 0; i < shapes.size(); i++) {
shapes[i]->draw();
shapes[i]->erase();
}
purge(shapes);
getchar();
} ///:~
输出
Circle::draw
Circle::erase
Square::draw
Square::erase
Square::draw
Square::erase
Circle::draw
Circle::erase
Circle::draw
Circle::erase
Circle::draw
Circle::erase
Square::draw
Square::erase
Circle::~Circle
Square::~Square
Square::~Square
Circle::~Circle
Circle::~Circle
Circle::~Circle
Square::~Square
工厂方法作为virtual create()出现在它自己的ShapeFactory类中
这是一个私有成员函数
意味着不能直接调用它
但可以被覆盖