参考书籍:
《设计模式:可复用面向对象软件的基础》
《Head First 设计模式》
参考课程:《C++设计模式》-李建忠
▷在软件系统中,经常面临着创建对象的工作;由于需求的变化,需要创建的对象的具体类型经常变化。
▷如何应对这种变化?如何绕过常规的对象创建方法(new),提供一种“封装机制”来避免客户程序和这种“具体对象创建工作”的紧耦合?
定义一个用于创建对象的接口,让子类决定实例化哪一个类。Factory Method使得一个类的实例化延迟(目的:解耦,手段:虚函数)到子类。
——《设计模式:可复用面向对象软件的基础》
场景:参照书籍-在建立披萨店之后,我们打算成立分店,建立不同风味的披萨店!
//PizzaStore.h#ifndef FACTORY_PIZZASTORE_H#define FACTORY_PIZZASTORE_H
#pragma once#include <string>#include "Pizza.h"
using namespace std;
//抽象工厂类class PizzaStore{public: PizzaStore(); ~PizzaStore();
virtual Pizza *orderPizza(string type);
//在PizzaStore里,"工厂方法"现在是抽象的。 virtual Pizza *createPizza(string type) = 0; //现在把工厂对象移到这个方法中。};
#endif //FACTORY_PIZZASTORE_H
//PizzaStore.cpp#include "PizzaStore.h"#include <utility>
PizzaStore::PizzaStore()= default;
PizzaStore::~PizzaStore()= default;
Pizza* PizzaStore::orderPizza(string type){ Pizza* pizza = createPizza(std::move(type)); //现在createPizza()方法从工厂对象中移回PizzaStore
pizza->prepare(); pizza->bake(); pizza->cut(); pizza->box();
return pizza;}
//Pizza.h#ifndef FACTORY_PIZZA_H#define FACTORY_PIZZA_H
#pragma once#include <string>#include <iostream>#include <vector>
using namespace std;
//抽象产品类class Pizza{protected: //每个披萨都具有名称(name)\面团类型(dough)\酱料类型(sauce)\一套佐料(toppings) string name; string dough; string sauce; vector<string> toppings;public: Pizza(); ~Pizza();
virtual void prepare(); virtual void bake(); virtual void cut(); virtual void box(); virtual string& getName();};
#endif //FACTORY_PIZZA_H
//Pizza.cpp#include "Pizza.h"
Pizza::Pizza()= default;
Pizza::~Pizza()= default;
void Pizza::prepare(){ //此抽象类提供了某些默认的基本做法,用来进行烘焙\切片\装盒 cout << "Preparing " << name << endl; cout << "Tossing dough..." << endl; cout << "Adding sauce..." << endl; cout << "Adding toppings: " << endl;
//准备工作需要以特定的顺序进行,有一连串的步骤 for(const auto & topping : toppings) { cout << " " << topping << endl; }}
//烘焙void Pizza::bake(){ cout << "Bake for 25 minutes at 350" << endl;}
//切片void Pizza::cut(){ cout << "Cutting the pizza into diagonal slices" << endl;}
//装盒void Pizza::box(){ cout << "Place pizza in official PizzaStore box" << endl;}
string& Pizza::getName(){ return name;}
//NYPizzaStore.h#ifndef FACTORY_NYPIZZASTORE_H#define FACTORY_NYPIZZASTORE_H
#pragma once#include "PizzaStore.h"#include "NYStyleCheesePizza.h"
//具体工厂类//NYPizzaStore扩展PizzaStore,所以拥有odrerPizza()方法(以及其他的方法);class NYPizzaStore : public PizzaStore{public: NYPizzaStore(); ~NYPizzaStore();
//createPizza()返回一个Pizza对象,由子类全权负责该实例化哪一个具体Pizza Pizza* createPizza(string item) override;};#endif //FACTORY_NYPIZZASTORE_H
//NYPizzaStore.cpp#include "NYPizzaStore.h"
NYPizzaStore::NYPizzaStore()= default;
NYPizzaStore::~NYPizzaStore()= default;
Pizza* NYPizzaStore::createPizza(string item){ if(item == "cheese") return new NYStyleCheesePizza;}
//NYStyleCheesePizza.h#ifndef FACTORY_NYSTYLECHEESEPIZZA_H#define FACTORY_NYSTYLECHEESEPIZZA_H
#pragma once#include "pizza.h"
//具体产品类1class NYStyleCheesePizza : public Pizza{public: NYStyleCheesePizza(); ~NYStyleCheesePizza();};
#endif //FACTORY_NYSTYLECHEESEPIZZA_H
//NYStyleCheesePizza.cpp#include "NYStyleCheesePizza.h"
NYStyleCheesePizza::NYStyleCheesePizza(){ //纽约披萨有自己的大葱番茄(Marinara)和薄饼。 name = "NY Style Sauce and Cheese Pizza"; dough = "Thin Crust Dough"; sauce = "Marinara Sauce";
//上面覆盖的是意大利Reggiano高级奶酪 toppings.emplace_back("Grated Reggiano Cheese");}
NYStyleCheesePizza::~NYStyleCheesePizza()= default;
//ChicagoPizzaStore.h#ifndef FACTORY_CHICAGOPIZZASTORE_H#define FACTORY_CHICAGOPIZZASTORE_H
#pragma once#include "PizzaStore.h"#include "ChicagoStyleCheesePizza.h"
class ChicagoPizzaStore : public PizzaStore{public: ChicagoPizzaStore(); ~ChicagoPizzaStore();
Pizza* createPizza(string type) override;};
#endif //FACTORY_CHICAGOPIZZASTORE_H
//ChicagoPizzaStore.cpp#include "ChicagoPizzaStore.h"
ChicagoPizzaStore::ChicagoPizzaStore()= default;
ChicagoPizzaStore::~ChicagoPizzaStore()= default;
Pizza* ChicagoPizzaStore::createPizza(std::string type){ if (type == "cheese") return new ChicagoStyleCheesePizza; return nullptr;}
//ChicagoStyleCheesePizza.h#ifndef FACTORY_CHICAGOSTYLECHEESEPIZZA_H#define FACTORY_CHICAGOSTYLECHEESEPIZZA_H
#pragma once#include "Pizza.h"
//具体产品类2class ChicagoStyleCheesePizza : public Pizza{public: ChicagoStyleCheesePizza(); ~ChicagoStyleCheesePizza();
void cut() override; //覆盖了cut方法};
#endif //FACTORY_CHICAGOSTYLECHEESEPIZZA_H
//ChicagoStyleCheesePizza.cpp#include "ChicagoStyleCheesePizza.h"
ChicagoStyleCheesePizza::ChicagoStyleCheesePizza(){ //芝加哥披萨使用小番茄作为酱料,并使用厚饼。 name = "Chicago Style Deep Fish Cheese Pizza"; dough = "Extra Thick Crust Dough"; sauce = "Plum Tomato Sauce";
//芝加哥风味的 深盘披萨使用许多意大利白干酪(mozzarella) toppings.emplace_back("Shredded Mozzarella Cheese");}
ChicagoStyleCheesePizza::~ChicagoStyleCheesePizza()= default;
void ChicagoStyleCheesePizza::cut(){ //这个芝加哥风味披萨覆盖了cut()方法,将披萨切成正方形 cout << "Cutting the pizza into square slices" << endl;}
//main.cpp//工厂方法模式定义了一个创建对象的接口,但由子类决定要实例化的类是哪一个。//工厂方法让类把实例化推迟到子类。//设计原则:要依赖抽象,不要依赖具体类#include <iostream>#include "NYPizzaStore.h"#include "ChicagoPizzaStore.h"
using namespace std;
//测试int main(){ //建立两个不同的店 NYPizzaStore nyStore; ChicagoPizzaStore chicagoStore;
Pizza *pizza = nyStore.orderPizza("cheese"); cout << "Ethan ordered a " << pizza->getName() << "\n" << endl; delete pizza;
pizza = chicagoStore.orderPizza("cheese"); cout << "Joel ordered a " << pizza->getName() << "\n" << endl; delete pizza;
return 0;}