实验4继承
实验任务2
task2.cpp
#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); }
同名覆盖原则:派生类和基类具有相同成员时,通过派生类对象访问,默认访问的是派生类的同名成员
二元作用域分辨符(::):用于显式指定使用的是哪个类的重名成员
类型兼容原则:派生类对象也可以当作基类对象来使用,但只能使用从基类继承的那部分功能调用虚函数时,根据指针实际指向的对象,选择相应的函数实现。
更改virtual后
实验任务3
使用类的组合和继承模拟简单的车辆信息管理。
Battery.hpp
#ifndef BATTERY_HPP #define BATTERY_HPP using namespace std; class Battery { private: int capacity; // (kWh) public: Battery(int cap=70):capacity(cap){} int get_capacity(){ return capacity; } }; #endif
Car.hpp
#ifndef CAR_HPP #define CAR_HPP #include <iostream> #include <string> using namespace std; class Car { private: string maker; //制造商 string model; //型号 int year; //生产年份 int odometers; //行车里程数 public: Car(){}; Car(string maker, string model, int year,int meters=0) : maker(maker), model(model), year(year), odometers(meters){}; void info() { cout << "制造商: " << maker << endl << "型号: " << model << endl << "生产年份: " << year << endl << "行车里程数: " << odometers << endl; } void update_odometers(int meters){ if (meters < odometers) cout << "new odometers is wrong!!!" << endl; else odometers = meters; } }; #endif
ElectricCar.hpp
#ifndef ELECTRICCAR_HPP #define ELECTRICCAR_HPP #include "Car.hpp" #include "Battery.hpp" using namespace std; class ElectricCar: public Car { private: Battery battery; public: ElectricCar(string maker, string model, int year,int cap=70): Car(maker, model, year), battery(cap){}; void info(){ Car::info(); cout << "电池: " << battery.get_capacity() << "kWh"<< endl; } }; #endif
task3.cpp'
#include <iostream> #include "ElectricCar.hpp" int main() { using namespace std; // test class of Car Car oldcar("Audi", "a404", 2048); cout << "--------oldcar's info--------" << endl; oldcar.update_odometers(25624); oldcar.info(); cout << endl; // test class of ElectricCar ElectricCar newcar("Tesla", "model sss", 2030); newcar.update_odometers(45646); cout << "\n--------newcar's info--------\n"; newcar.info(); }
测试结果:
实验任务4
使用类的继承,模拟简单的机器宠物。
pets.hpp
#ifndef PETS_HPP #define PETS_HPP using namespace std; class MachinePets { public: MachinePets(const string s) : nickname{s} {} string get_nickname() const { return nickname; } virtual string talk() { return "ze~ze~"; } private: string nickname; }; class PetCats : public MachinePets { public: PetCats(const string s) : MachinePets(s) {} string talk() { return "miao wu~"; } }; class PetDogs : public MachinePets { public: PetDogs(const string s) : MachinePets(s) {} string talk() { return "wang wang~"; } }; #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); }
测试结果:
总结与体会
1、派生类构造函数初始化,通过参数化列表,先调用基类构造函数初始化基类,再初始化派生类成员
2、有默认值的形参才可以没有实参