Java中继承、多态、重载和重写介绍(5)

时间:2014-08-01 02:59来源:网络整理作者:网络点击: 次

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例6 #include iostreamusing namespace std; class Base{public: virtual void fun() { cout "Base::fun()" endl; }//overload virtual void fun(int i) { cout "Base::fun(int i)" endl; }//overload}; class Deri

例6

#include <iostream>
using namespace std;
 
class Base{
public:
     virtual void fun() { cout << "Base::fun()" << endl; }//overload
  virtual void fun(int i) { cout << "Base::fun(int i)" << endl; }//overload
};
 
class Derive : public Base{
public:
     void fun() { cout << "Derive::fun()" << endl; }//override
  void fun(int i) { cout << "Derive::fun(int i)" << endl; }//override
     void fun(int i,int j){ cout<< "Derive::fun(int i,int j)" <<endl;}//overload
};
 
int main()
{
 Base *pb = new Derive();
 pb->fun();
 pb->fun(1);
 //下面一句错误，故屏蔽掉
 //pb->fun(1,2);virtual函数不能进行overload,error C2661: 'fun' : no overloaded function takes 2 parameters
 
 cout << endl;
 Derive *pd = new Derive();
 pd->fun();
 pd->fun(1);
 pd->fun(1,2);//overload
 
 delete pb;
 delete pd;
 return 0;
}
/*

输出结果

Derive::fun()
Derive::fun(int i)

Derive::fun()
Derive::fun(int i)
Derive::fun(int i,int j)
Press any key to continue
*/

例7-1

#include <iostream> 
using namespace std;
 
class Base{
public:
     virtual void fun(int i){ cout <<"Base::fun(int i)"<< endl; }
};
 
class Derive : public Base{};
 
int main()
{
     Base *pb = new Derive();
     pb->fun(1);//Base::fun(int i)
     delete pb;
     return 0;
}

例7-2

#include <iostream> 
using namespace std;
 
class Base{
public:
     virtual void fun(int i){ cout <<"Base::fun(int i)"<< endl; }
};
 
class Derive : public Base{
public:
  void fun(double d){ cout <<"Derive::fun(double d)"<< endl; } 
};
 
int main()
{
     Base *pb = new Derive();
     pb->fun(1);//Base::fun(int i)
     pb->fun((double)0.01);//Base::fun(int i)
     delete pb;
     return 0;
}

例8-1

#include <iostream> 
using namespace std;
 
class Base{
public:
     virtual void fun(int i){ cout <<"Base::fun(int i)"<< endl; }
};
 
class Derive : public Base{
public:
     void fun(int i){ cout <<"Derive::fun(int i)"<< endl; }
};
 
int main()
{
     Base *pb = new Derive();
     pb->fun(1);//Derive::fun(int i)
     delete pb;
     return 0;
}

例8-2

#include <iostream> 
using namespace std;
 
class Base{
public:
     virtual void fun(int i){ cout <<"Base::fun(int i)"<< endl; }
};
 
class Derive : public Base{
public:
     void fun(int i){ cout <<"Derive::fun(int i)"<< endl; }
     void fun(double d){ cout <<"Derive::fun(double d)"<< endl; }     
};
 
int main()
{
     Base *pb = new Derive();
     pb->fun(1);//Derive::fun(int i)
     pb->fun((double)0.01);//Derive::fun(int i)
     delete pb;
     return 0;
}

例9

#include <iostream> 
using namespace std;
 
class Base{
public:
     virtual void fun(int i){ cout <<"Base::fun(int i)"<< endl; }

};
class Derive : public Base{
public:
    void fun(int i){ cout <<"Derive::fun(int i)"<< endl; }
    void fun(char c){ cout <<"Derive::fun(char c)"<< endl; } 
    void fun(double d){ cout <<"Derive::fun(double d)"<< endl; }     
};
int main()
{
     Base *pb = new Derive();
     pb->fun(1);//Derive::fun(int i)
     pb->fun('a');//Derive::fun(int i)
     pb->fun((double)0.01);//Derive::fun(int i)
 
     Derive *pd =new Derive();
     pd->fun(1);//Derive::fun(int i)
     //overload
     pd->fun('a');//Derive::fun(char c)     
     //overload
     pd->fun(0.01);//Derive::fun(double d)     
 
     delete pb;
     delete pd;
     return 0;
}

例7-1和例8-1很好理解，我把这两个例子放在这里，是让大家作一个比较摆了，也是为了帮助大家更好的理解：
n          例7-1中，派生类没有覆盖基类的虚函数，此时派生类的vtable中的函数指针指向的地址就是基类的虚函数地址。
n          例8-1中，派生类覆盖了基类的虚函数，此时派生类的vtable中的函数指针指向的地址就是派生类自己的重写的虚函数地址。
在例7-2和8-2看起来有点怪怪，其实，你按照上面的原则对比一下，答案也是明朗的：
n          例7-2中，我们为派生类重载了一个函数版本：void fun(double d) 其实，这只是一个障眼法。我们具体来分析一下，基类共有几个函数，派生类共有几个函数：
类型
基类
派生类

Vtable部分
void fun(int i)
指向基类版的虚函数void fun(int i)

静态部分

void fun(double d)