C++ 的多态

//我们先定义三个类 都非常的简单就一个函数进行打印类的名字,father和mather公开继承Object类
class ObjectFactory {
public:
    void show() {
        cout << "baseFactory show" << endl;
    }
};


class FatherFactory : public ObjectFactory {
public:
    void show() {
        cout << "FatherFactory show" << endl;
    }
};

class MatherFactory : public ObjectFactory {
public:
    void show() {
        cout << "MatherFactory show" << endl;
    }
};


void show(ObjectFactory *objectFactory) {
    objectFactory->show();
}

第一种情况

 FatherFactory *fatherFactory = new FatherFactory();
    MatherFactory* matherFactory = new MatherFactory();

    show(fatherFactory);
    show(matherFactory);
    

结果
baseFactory show
baseFactory show

以上代码在Java中执行的肯定是可以分辨出我们想要执行那个函数,但是C++执行的全部都是Object类的show函数

第二种情况

ObjectFactory *fatherFactory = new FatherFactory();
    ObjectFactory* matherFactory = new MatherFactory();

    show(fatherFactory);
    show(matherFactory);

这种情况应该执行各自函数了把?但是结果还是让我们大跌眼镜

结果
baseFactory show
baseFactory show

依旧是执行的Object类的函数

总结:
由此我们可以得出结论C++ 默认是关闭多态功能的,Java是默认支持多态函数的,但是我们怎么开启C++的多态呢

我们利用关键字virtual来修饰我们的Object的show函数-----称之为虚函数

如代码

class ObjectFactory {
public:
    virtual void show() {
        cout << "baseFactory show" << endl;
    }
};

//仅有Object的show函数添加  virtual 关键字 其他类不变

执行代码

 //第一种情况
    FatherFactory *fatherFactory = new FatherFactory();
    MatherFactory* matherFactory = new MatherFactory();

    show(fatherFactory);
    show(matherFactory);


    cout << endl;
    //第二种情况
    ObjectFactory *fatherFactory1 = new FatherFactory();
    ObjectFactory* matherFactory1 = new MatherFactory();

    show(fatherFactory1);
    show(matherFactory1);

来我们看结果
FatherFactory show
MatherFactory show

FatherFactory show
MatherFactory show

到此C++的多态执行成功