P493 brass

实现多态共有继承的两种方法

1 在派生类中重新定义基类的方法

2 使用虚方法

P493程序清单13.7使用的方法为在派生类中重新定义基类的方法

brass.h

#ifndef BRASS_H
#define BRASS_H
#include <string>
class Brass{
private:
    std::string fullName;  //客户姓名
    long acctNum;  //账号
    double balance;  //当前结余
public:
    Brass(const std::string & s="Nullbody",long an=-1,
          double bal=0.0);
    void Deposit(double amt);  //存款
    virtual void withdraw(double amt);  //取款
    double Balance() const; //显示余额
    virtual void ViewAcct() const;
    virtual ~Brass() {}
};
//Brass Plus Account Class
class BrassPlus:public Brass
{
private:
    double maxLoan;  //透支的上线
    double rate;  //透支贷款利率
    double owesBank;  //当前的透支额度
public:
    BrassPlus(const std::string &s="Nullbody",long an=-1,
              double bal=0.0,double ml=500,double r=0.11125);
    BrassPlus(const Brass &ba,double ml=500,
                              double r=0.11125);
    virtual void ViewAcct() const;
    virtual void withdraw(double amt);
    void ResetMax(double m){maxLoan=m;};
    void ResetRate(double r){rate=r;};
    void ResetOwes() {owesBank=0;};
};
#endif // BRASS_H

main.cpp

#include <iostream>
#include "brass.h"
using namespace std;
//formatting stuff
typedef std::ios_base::fmtflags format;
typedef std::streamsize precis;
format setFormat();
void restore(format f,precis p);
//Brass methods
Brass::Brass(const string &s, long an, double bal)
{
    fullName=s;
    acctNum=an;
    balance=bal;
}
//储蓄函数
void Brass::Deposit(double amt)
{
    if(amt<0)
    {
        cout<<"Negative deposit not allowed;"
           <<"deposit is cancelled\n";
    }
    else
        balance=balance+amt;
}
void Brass::withdraw(double amt)
{
    //set up ###.##format
    format initialState=setFormat();
    precis prec=cout.precision(2);
    if(amt<0)
    {
        cout<<"withdrawal amouut must be positive;"
           <<"withdrawal canceled\n";
    }
    else if(amt<=balance)
    {
        balance=balance-amt;
    }
    else
    {
        cout<<"withrdrawl amout of $"<<amt
           <<" exceeds your balance\n"
          <<"withdrawal canceled\n";
    }
    restore(initialState,prec);
}
double Brass::Balance() const
{
    return balance;
}
void Brass::ViewAcct() const
{
    //set up ###.## format
    format initialState=setFormat();
    precis prec=cout.precision(2);
    cout<<"Client:"<<fullName<<endl;
    cout<<"Account Number:"<<acctNum<<endl;
    cout<<"Balance:$"<<balance<<endl;
    restore(initialState,prec);  //存储原始的格式
}
//BrassPlus的方法
BrassPlus::BrassPlus(const string &s,
                     long an, double bal,
                     double ml, double r):Brass(s,an,bal)
{
    //构造函数
    maxLoan=ml;
    owesBank=0.0;
    rate=r;
}
BrassPlus::BrassPlus(const Brass &ba, double ml, double r):Brass(ba)
{
    maxLoan=ml;
    owesBank=0.0;
    rate=r;
}
//重定义
void BrassPlus::ViewAcct() const
{
    //set up ###.##format
    format initialState=setFormat();
    precis prec=cout.precision(2);
    Brass::ViewAcct();  //显示基类的部分
    cout<<"Maximum loan:$"<<maxLoan<<endl;
    cout<<"Owed to back:$"<<owesBank<<endl;
    cout.precision(3);
    cout<<"Loan Rate"<<100*rate<<"%\n";
    restore(initialState,prec);
}
//重定义
//如果用户提取的金额超过了结余，该方法将安排贷款
void BrassPlus::withdraw(double amt)
{
    format initialState=setFormat();
    precis prec=cout.precision(2);
    //使用Balance()函数来确定结余
    double bal=Balance();
    if(amt<=bal)
    {
        //提款少于存款，提款成功
        Brass::withdraw(amt);  //继承类中调用基类的方法
    }
    else if(amt<=bal+maxLoan-owesBank)
    {
        double advance=amt-bal;
        owesBank+=advance*(1.0+rate);  //owesBank当前的透支额度
        cout<<"Bank advance:$"<<advance<<endl;
        cout<<"Finance charge:$"<<advance*rate<<endl;
        Deposit(advance);  //放贷
        //放贷成功后可以今天提款
        Brass::withdraw(amt);
    }
    else
    {
        cout<<"Credit limit exceeded.Transaction cancelled.\n";
    }
    restore(initialState,prec);
}
format setFormat()
{
    //set up ###.## format
    return cout.setf(std::ios_base::fixed,
                     std::ios_base::floatfield);
}
void restore(format f, precis p)
{
    cout.setf(f,std::ios_base::floatfield);
    cout.precision(p);
}
int main(int argc, char *argv[])
{
    cout << "Hello World!" << endl;
    using std::cout;
    using std::endl;
    Brass Piggy("Procelot Pigg",381299,4000.00);
    BrassPlus Hoggy("Horatio Hogg",382288,3000.00);
    Piggy.ViewAcct();
    cout<<endl;
    Hoggy.ViewAcct();
    cout<<"Depositing $1000 into the Hogg Account:\n";
    Hoggy.Deposit(1000.00);  //储蓄1000元到Hoggy的账户
    cout<<"New Balance:$"<<Hoggy.Balance()<<endl;
    cout<<"Withdrawing $4200 from the Pigg Account:\n";
    //取款失败，且不能借贷，因为Piggy是基类的对象，没有实现借贷的方法
    Piggy.withdraw(4200.00);
    cout<<"Pigg account balance:$"<<Piggy.Balance()<<endl;
    cout<<"Withdrwaing $42000 from the Hogg Account:\n";
    Hoggy.withdraw(4200.00);
    Hoggy.ViewAcct();
    return 0;
}

运行结果如下



IDE为Qt Creator 4.0.3 (Community)