c++ day15 抽象类&多态原理&代码复用可拓展

• 纯虚函数和抽象类
• 纯虚函数是一个在基类中说明的虚函数，在基类中没有定义，要求任何派生类都定义自己的版本
• 纯虚函数为各派生类提供一公共界面，（接口的封装和设计，软件的模块功能划分）
• 纯虚函数说明形式
•            virtual 类型 函数名（参数表） =0；
• 一个具有纯虚函数的基类称为抽象类
• 虚函数类不可以直接建立对象，但是可以建立类指针

返回值可以是指针或者引用， 但是不可以是抽象元素

---

---

• #include <iostream>
  using namespace std;
  //构造函数中调用虚函数能发生多态么
  
  //解耦合。。。模块的划分
  class Figure{
  public:
  	//提供一个统一的接口
  	virtual void getArea()=0;//纯虚函数，抽象类
  protected:
  private:
  
  };
  class Circle : public Figure {
  public:
  	Circle(int a,int b )
  	{
  		this->a = a;
  		this->b = b;
  	}
  	virtual void getArea()
  	{
  		cout<<"圆形的面积"<<a*a*3.14<<endl;
  	}
  protected:
  private:
  	int a;
  	int b;
  };
  class Square : public Figure {
  public:
  	Square(int a,int b )
  	{
  		this->a = a;
  		this->b = b;
  	}
  	virtual void getArea()
  	{
  		cout<<"矩形的面积"<<a*b<<endl;
  	}
  protected:
  private:
  	int a;
  	int b;
  };
  class Tri : public Figure {
  public:
  	Tri(int a,int b )
  	{
  		this->a = a;
  		this->b = b;
  	}
  	virtual void getArea()
  	{
  		cout<<"直角三角形的面积"<<0.5*a*b<<endl;
  	}
  protected:
  private:
  	int a;
  	int b;
  };
  //构造一个方法，给多态提供方法
  void showlife(Figure *f){
  	f->getArea();
  }
  
  void main(){
  
  	//Figure p;//报错，抽象类不能被实例化
  	Figure *base = NULL;//声明指针是可以的
  
  	Circle c1(10,20);
  	Tri t1(3,4);
  	Square s1(6,6);
  
  	//面向抽象接口编程
  	showlife(&c1);
  	showlife(&t1);
  	showlife(&s1);
  
  	cout<<"hello"<<endl;
  	system("pause");
  	return ;
  }
  
  

---

• 有关多继承的说明
• 工程上的多继承
  • 被实际开发经验抛弃的多继承
  • 工程开发中真正意义上的多继承是几乎不被使用的
  • 多重继承带来的代码复杂性远多于其带来的便利
  • 多重继承对代码维护性上的影响是灾难性的
  • 在设计方法上，任何多继承都可以用单继承代替
  • C++中是否有java中的接口概念?
    • 绝大多数面向对象语言都不支持多继承
    • 绝大多数面向对象语言都支持接口的概念
    • c++中没有接口概念
    • c++中可以使用纯虚函数实现接口
    • 接口类只定义函数原型，不定义任何数据
    • 多重继承接口不会带来二义性和复杂性等问题

#include <iostream>
using namespace std;
class Interface1
{
public:
	virtual int add(int a,int b )=0;
	virtual void print()=0;
};
class Interface2
{
public:
	virtual int multi(int a,int b)=0;
	virtual void print()=0;
};
class Parent
{
public:
	int getA(){
		a = 0;
		return a;
	}
protected:
private:
	int a;
};
class Child : public Parent,public Interface1,public Interface2{
public:
	virtual int add(int a,int b )
	{
		cout<<"child add（）"<<endl;
		return a+b;
	}
	virtual void print()
	{
		cout<<"child print（）"<<endl;
	}
	virtual int multi(int a,int b)
	{
		cout<<"child multi（）"<<endl;
		return a*b;
	}
protected:
private:
};
void main(){
	Child c1;
	c1.print();
	Interface1 *i1 = &c1;
	i1->add(1,2);

	Interface2 *i2 = &c1;
	i2->multi(4,4);


	cout<<"hello"<<endl;
	system("pause");
	return ;
}

---

• 代码复用，可拓展

• #include <iostream>
  using namespace std;
  
  class programmer
  {
  public:
  	virtual void getSal()=0;
  };
  class juniorp:public programmer
  {
  public:
  	juniorp(char *name,char *job,int sal)
  	{
  		this->name = name;
  		this->job = job;
  		this->sal = sal;
  	}
  	virtual void getSal()
  	{
  		cout<<name<<" "<<job<<" "<<sal<<endl;
  	}
  protected:
  private:
  	char *name;
  	char *job;
  	int sal;
  };
  class mid_programmer:public programmer
  {
  public:
  	mid_programmer(char *name,char *job,int sal)
  	{
  		this->name = name;
  		this->job = job;
  		this->sal = sal;
  	}
  	virtual void getSal()
  	{
  		cout<<name<<" "<<job<<" "<<sal<<endl;
  	}
  protected:
  private:
  	char *name;
  	char *job;
  	int sal;
  };
  class adv_programmer:public programmer
  {
  public:
  	adv_programmer(char *name,char *job,int sal)
  	{
  		this->name = name;
  		this->job = job;
  		this->sal = sal;
  	}
  	virtual void getSal()
  	{
  		cout<<name<<" "<<job<<" "<<sal<<endl;
  	}
  protected:
  private:
  	char *name;
  	char *job;
  	int sal;
  };
  class architect:public programmer
  {
  public:
  	architect(char *name,char *job,int sal)
  	{
  		this->name = name;
  		this->job = job;
  		this->sal = sal;
  	}
  	virtual void getSal()
  	{
  		cout<<name<<" "<<job<<" "<<sal<<endl;
  	}
  protected:
  private:
  	char *name;
  	char *job;
  	int sal;
  };
  void CalProSal(programmer *base){
  
  	base->getSal();
  
  }
  void main(){
  	mid_programmer mp("yj","中级程序员",8600);
  	juniorp jp("zk","初级程序员",3000);
  	adv_programmer ap ("hz","高级程序员",50000);
  	architect at("qp","架构师",100000);
  	CalProSal(&jp);
  	CalProSal(&ap);
  	CalProSal(&mp);
  	CalProSal(&at);
  
  	cout<<"hello"<<endl;
  	system("pause");
  	return ;
  }