目录
- 简单工厂
- 工厂方法模式
简单工厂
定义:简单工厂由一个工厂根据参数类型决定创建哪种产品的实例。
简单工厂不包含在23种设计模式之内(简单工厂不满足开闭原则,后面会详细讲)
举例:张三去4S店买了车,显而易见,车不是张三造出来的,车是工厂造出来的,张三获得了该车并能够使用该车,但是造车的细节张三不用知道。
铁蛋在一家汽车工厂上班,这家工厂承接了”小米汽车“和”华为汽车“的生产,一天铁蛋接到了要求,要新开一个”长安汽车“生产线生产长安汽车,铁蛋要怎么做呢?
先写一个简单工厂的例子,再看看铁蛋要怎么做?
简单工厂模式有三个角色:抽象基类(Car)
实现类(XiaoMiCar、HuaWeiCar)
简单工厂类(SimpleFactory)
#include <iostream>
#include <string>
using namespace std;
//抽象基类
class Car
{
public:
Car(string name) : name_(name) {}
virtual void Show() = 0;
protected:
string name_;
};
//实现类
class XiaomiCar : public Car {
public:
XiaomiCar(string name) : Car(name) {}
void Show() {
cout << "获得一辆小米轿车: " << name_ << endl;
}
};
//实现类
class HuaweiCar : public Car {
public:
HuaweiCar(string name) : Car(name) {}
void Show() {
cout << "获得一辆华为轿车: " << name_ << endl;
}
};
enum CarType
{
XIAOMI, HUAWEI
};
//简单工厂类
class SimpleFactory {
public:
Car* CreateCar(CarType type) {
switch (type) {
case XIAOMI:
return new XiaomiCar("SU7");
case HUAWEI:
return new HuaweiCar("问界");
default:
return nullptr;
}
}
};
int main()
{
SimpleFactory* factory = new SimpleFactory();
Car* c1 = factory->CreateCar(XIAOMI);
Car* c2 = factory->CreateCar(HUAWEI);
c1->Show();
c2->Show();
delete c1;
delete c2;
delete factory;
}
运行结果:
上面小米汽车XiaomiCar 和华为汽车HuaweiCar 继承了汽车基类Car。
简单工厂SimpleFactory根据传入不同类型CarType来生产不同类型的车。
你是否想到了铁蛋要怎么做,铁蛋是这样做的:
1.增加长安汽车类(继承了汽车基类Car)
2.修改简单工厂类SimpleFactory(增加”CHANGAN“类型车的创建)
#include <iostream>
#include <string>
using namespace std;
class Car
{
public:
Car(string name) : name_(name) {}
virtual void Show() = 0;
protected:
string name_;
};
class XiaomiCar : public Car {
public:
XiaomiCar(string name) : Car(name) {}
void Show() {
cout << "获得一辆小米轿车: " << name_ << endl;
}
};
class HuaweiCar : public Car {
public:
HuaweiCar(string name) : Car(name) {}
void Show() {
cout << "获得一辆华为轿车: " << name_ << endl;
}
};
class ChanganCar : public Car {
public:
ChanganCar(string name) : Car(name) {}
void Show() {
cout << "获得一辆长安轿车: " << name_ << endl;
}
};
enum CarType
{
XIAOMI, HUAWEI, CHANGAN
};
class SimpleFactory {
public:
Car* CreateCar(CarType type) {
switch (type) {
case XIAOMI:
return new XiaomiCar("SU7");
case HUAWEI:
return new HuaweiCar("问界");
case CHANGAN:
return new ChanganCar("深蓝《偷偷藏不住》");
default:
return nullptr;
}
}
};
int main()
{
cout << "------简单工厂------" << endl;
SimpleFactory* factory = new SimpleFactory();
Car* c1 = factory->CreateCar(XIAOMI);
Car* c2 = factory->CreateCar(HUAWEI);
Car* c3 = factory->CreateCar(CHANGAN);
c1->Show();
c2->Show();
c3->Show();
delete c1;
delete c2;
delete c3;
delete factory;
}
运行结果:
成功生产了长安轿车!
但是从逻辑上来讲,同一个工厂不会生产小米汽车又生产华为汽车,又或者这个工厂还将生产长安汽车
因为:当简单工厂想增加生产长安汽车时,会修改简单工厂类SimpleFactory(增加”CHANGAN“类型车的创建),违反了开闭原则(对修改关闭,对扩展开放)。每当我们增加一种产品的时候就要去修改工厂方法,这样会破坏其内聚性,给维护带来额外开支。
所以,有了工厂方法模式来解决该问题。
工厂方法模式
定义:工厂基类负责定义创建对象的公共接口,子类工厂负责创建出具体的对象,来实现不同产品的工厂化创建。
设计模式有三大分类:创建型模式、结构型模式、行为型模式
工厂方法模式属于创建型模式
工厂方法模式不只有一个工厂,每个工厂只生产一种特定的产品。这样做的好处是当以后需要增加新的产品时,直接新增加一个对应的工厂就可以,而不是去修改原有的工厂,符合编程原则的开闭原则。
#include <iostream>
#include <string>
using namespace std;
class Car
{
public:
Car(string name) : name_(name) {}
virtual void Show() = 0;
protected:
string name_;
};
class XiaomiCar : public Car {
public:
XiaomiCar(string name) : Car(name) {}
void Show() {
cout << "获得一辆小米轿车: " << name_ << endl;
}
};
class HuaweiCar : public Car {
public:
HuaweiCar(string name) : Car(name) {}
void Show() {
cout << "获得一辆华为轿车: " << name_ << endl;
}
};
class Factory {
public:
virtual Car* CreateCar(string name) = 0;
};
class XiaomiFactory : public Factory
{
public:
Car* CreateCar(string name)
{
return new XiaomiCar(name);
}
};
class HuaweiFactory : public Factory
{
public:
Car* CreateCar(string name)
{
return new HuaweiCar(name);
}
};
int main()
{
cout << "------工厂方法模式------" << endl;
Factory* xiaomiFactory = new XiaomiFactory();
Factory* huaweiFactory = new HuaweiFactory();
Car* xiaomiCar = xiaomiFactory->CreateCar("SU7");
Car* huaweiCar = huaweiFactory->CreateCar("问界");
xiaomiCar->Show();
huaweiCar->Show();
delete xiaomiCar;
delete huaweiCar;
delete xiaomiFactory;
delete huaweiFactory;
}
运行结果:
同样上面小米汽车XiaomiCar 和华为汽车HuaweiCar 继承了汽车基类Car。
小米工厂XiaomiFactory和华为工厂HuaweiFactory继承了工厂基类Factory。
小米工厂生产小米汽车,华为工厂生产华为汽车。
这样,铁蛋想生产”长安汽车“,就直接新建长安汽车工厂,由长安工厂来生产长安汽车,这样就不用修改小米工厂和华为工厂,满足程序设计的开闭原则。
铁蛋是这样做的:
1.增加了长安汽车类ChanganCar (继承了汽车基类Car)
2.增加了长安汽车工厂ChanganFactory (继承了工厂基类Factory)
#include <iostream>
#include <string>
using namespace std;
class Car
{
public:
Car(string name) : name_(name) {}
virtual void Show() = 0;
protected:
string name_;
};
class XiaomiCar : public Car {
public:
XiaomiCar(string name) : Car(name) {}
void Show() {
cout << "获得一辆小米轿车: " << name_ << endl;
}
};
class HuaweiCar : public Car {
public:
HuaweiCar(string name) : Car(name) {}
void Show() {
cout << "获得一辆华为轿车: " << name_ << endl;
}
};
class Factory {
public:
virtual Car* CreateCar(string name) = 0;
};
class XiaomiFactory : public Factory
{
public:
Car* CreateCar(string name)
{
return new XiaomiCar(name);
}
};
class HuaweiFactory : public Factory
{
public:
Car* CreateCar(string name)
{
return new HuaweiCar(name);
}
};
class ChanganCar : public Car {
public:
ChanganCar(string name) : Car(name) {}
void Show() {
cout << "获得一辆长安轿车: " << name_ << endl;
}
};
class ChanganFactory : public Factory
{
public:
Car* CreateCar(string name)
{
return new ChanganCar(name);
}
};
int main()
{
cout << "------工厂方法模式------" << endl;
Factory* xiaomiFactory = new XiaomiFactory();
Factory* huaweiFactory = new HuaweiFactory();
Factory* changanFactory = new ChanganFactory();
Car* xiaomiCar = xiaomiFactory->CreateCar("SU7");
Car* huaweiCar = huaweiFactory->CreateCar("问界");
Car* changanCar = changanFactory->CreateCar("深蓝《偷偷藏不住》");
xiaomiCar->Show();
huaweiCar->Show();
changanCar->Show();
delete xiaomiCar;
delete huaweiCar;
delete changanCar;
delete xiaomiFactory;
delete huaweiFactory;
delete changanFactory;
}
运行结果:
无广告,以汽车为例故事形式介绍了简单工厂和工厂方法模式。
谢谢观看,祝顺利!