实验4 继承

四、实验结论

2. 实验任务2

程序源码:

#include <iostream>
#include <typeinfo>

// definitation of Graph
class Graph
{
public:
    void draw() { std::cout << "Graph::draw() : just as an interface\n"; }
};


// definition of Rectangle, derived from Graph
class Rectangle : public Graph
{
public:
    void draw() { std::cout << "Rectangle::draw(): programs of draw a rectangle\n"; }
};


// definition of Circle, derived from Graph
class Circle : public Graph
{
public:
    void draw() { std::cout << "Circle::draw(): programs of draw a circle\n"; }
};


// definitaion of fun(): as a call interface
void fun(Graph *ptr)
{
    std::cout << "pointer type: " << typeid(ptr).name() << "\n";
    std::cout << "RTTI type: " << typeid(*ptr).name() << "\n";
    ptr -> draw();
}

// test 
int main()
{
    Graph g1;
    Rectangle r1;
    Circle c1;

    // call by object name
    g1.draw();
    r1.draw();
    c1.draw();

    std::cout << "\n";

    // call by object name, and using the scope resolution operator::
    r1.Graph::draw();
    c1.Graph::draw();

    std::cout << "\n";

    // call by pointer to Base class
    fun(&g1);
    fun(&r1);
    fun(&c1);
}

 

运行结果截图:

 

归纳总结:

1.同名覆盖原则：

（1）派生类与基类中有相同成员时，若未强行指名，则通过派生类对象使用的是派生类的同名成员。

（2）如果要通过派生类的对象访问基类被覆盖的同名成员，需要加 对象名.基类名::同名成员 来限定。

2.二元作用域分辨符：

（1）如果派生类中声明了与基类成员函数同名的新函数，及时函数的参数表不同，从基类继承的同名函数的所有重载形式也都会被隐藏。

（2）如果某派生类的多个基类拥有同名的成员，同时，派生类又新增这样的同名成员，在这种情况下，派生类的成员将隐藏所有基类的同名成员。

3.类型兼容原则：

在需要基类对象的任何地方，都可以使用公有派生类的对象来替代。

 

代码微调后，运行结果截图:

 

3. 实验任务3

battery.hpp:

#ifndef BATTERY_HPP
#define BATTERY_HPP

#include<iostream>

class Battery{
    public:
        Battery() {capacity=70;}
        int get_capacity() {return capacity;}
    private:
        int capacity;
};

#endif

 

car.hpp:

#ifndef CAR_HPP
#define CAR_HPP

#include<iostream>

using namespace std;

class Car{
    public:
        Car(string a,string b,int c): maker(a),model(b),year(c) {odometers=0;}
        void info();
        void update_odometers(int t);
    private:
        string maker,model;
        int year,odometers;
};

void Car::info(){
    cout << "制造商  :" << maker << endl;
    cout << "型号    :" << model << endl;
    cout << "生产年份:" << year << endl;
    cout << "里程数  :" << odometers << endl;
}

void Car::update_odometers(int t){
    if(t<odometers){
        cout << "更新数值有误" << endl;
        return;
    }
    else{
        odometers=t;
    }
}

#endif

 

electricCar.hpp:

#ifndef ELECTRICCAR_HPP
#define ELECTRICCAR_HPP

#include"car.hpp"
#include"battery.hpp"
#include<iostream>

using namespace std;

class ElectricCar:public Car{
    public:
        ElectricCar(string a,string b,int c): Car(a,b,c) {}
        void info();
    private:
        Battery battery;
};

void ElectricCar::info(){
    Car::info();
    cout << "µç³ØÈÝÁ¿:" << battery.get_capacity() << "-kWh" << endl;
}

#endif

 

task3.cpp:

#include <iostream>
#include "electricCar.hpp"

int main()
{
    using namespace std;

    // test class of Car
    Car oldcar("ABC", "xx", 2019);
    cout << "--------oldcar's info--------" << endl;
    oldcar.update_odometers(15000);
    oldcar.info();

    cout << endl;

    // test class of ElectricCar
    ElectricCar newcar("XYZ", "s", 2018);
    newcar.update_odometers(5000);
    cout << "\n--------newcar's info--------\n";
    newcar.info();
}

 

运行测试截图:

 

4. 实验任务4

pets.hpp:

#ifndef PETS_HPP
#define PETS_HPP

#include<iostream>

using namespace std;

class MachinePets{
    public:
        MachinePets(const string s): nickname(s) {}
        virtual string talk() {return "";}
        string get_nickname() {return nickname;}
    private:
        string nickname;
};

class PetCats: public MachinePets{
    public:
        PetCats(const string s): MachinePets(s) {}
        string talk(){return "喵~";}
};

class PetDogs: public MachinePets{
    public:
        PetDogs(const string s): MachinePets(s) {}
        string talk(){return "汪！";}
};

#endif

 

task4.cpp:

#include <iostream>
#include "pets.hpp"

void play(MachinePets *ptr)
{
    std::cout << ptr->get_nickname() << " says " << ptr->talk() << std::endl;
}

int main()
{
    PetCats cat("miku");
    PetDogs dog("da huang");

    play(&cat);
    play(&dog);
}

 

运行测试截图: