Object-Oriented Programming (OOP) and Inheritance

Object-Oriented Programming (OOP) and Inheritance

1 The features of OOP

There are lots of definitions for OOP, but 3 primary features of it are:
• Encapsulation: grouping related data and functions together as objects and defining an interface to those objects.

• Inheritance: allowing code to be reused between related types.

• Polymorphism: allowing a value to be one of several types, and determining at runtime which functions to call on it based on its type.

1.1 Encapsulation

Encapsulation just refers to packaging related stuff together.

1.1.1 simple base class(a table-tennis base class)

// tabtenn0.h -- a table-tennis base class
#ifndef TABTENN0_H_
#define TABTENN0_H_
#include 
using std::string;
// simple base class
class TableTennisPlayer
{
private:
    string firstname;
    string lastname;
    bool hasTable;
public:
    TableTennisPlayer (const string & fn = "none",
                       const string & ln = "none", bool ht = false);
    void Name() const;
    bool HasTable() const { return hasTable; };
    void ResetTable(bool v) { hasTable = v; };
};
#endif

1.1.2 simple base class mothods (a table-tennis base classs mothods)

//tabtenn0.cpp -- simple base-class methods
#include "tabtenn0.h"
#include 

TableTennisPlayer::TableTennisPlayer (const string & fn, 
    const string & ln, bool ht) : firstname(fn),
       lastname(ln), hasTable(ht) {}
    
void TableTennisPlayer::Name() const
{
    std::cout << lastname << ", " << firstname;
}

1.1.3 using a base class

// usett0.cpp -- using a base class
#include 
#include "tabtenn0.h"

int main ( void )
{
    using std::cout;
    TableTennisPlayer player1("Chuck", "Blizzard", true);
    TableTennisPlayer player2("Tara", "Boomdea", false);
    player1.Name();
    if (player1.HasTable())
        cout << ": has a table.\n";
    else
        cout << ": hasn't a table.\n";
    player2.Name();
    if (player2.HasTable())
        cout << ": has a table";
    else
        cout << ": hasn't a table.\n";
    // std::cin.get();
    return 0;
}

the output of the program：

Blizzard, Chuck: has a table.
Boomdea, Tara: hasn’t a table.

1.2 Inheritance

allowing code to be reused between related types。Inheritance allows us to define hierarchies of related classes.

• includes the point ratings (加入比分)

1.2.1 table-tennis base classes

// tabtenn1.h -- a table-tennis base class
#ifndef TABTENN1_H_
#define TABTENN1_H_
#include 
using std::string;
// simple base class
class TableTennisPlayer
{
private:
    string firstname;
    string lastname;
    bool hasTable;
public:
    TableTennisPlayer (const string & fn = "none",
                       const string & ln = "none", bool ht = false);
    void Name() const;
    bool HasTable() const { return hasTable; };
    void ResetTable(bool v) { hasTable = v; };
};

// simple derived class
class RatedPlayer : public TableTennisPlayer
{
private:
    unsigned int rating;
public:
    RatedPlayer (unsigned int r = 0, const string & fn = "none",
                 const string & ln = "none", bool ht = false);
    RatedPlayer(unsigned int r, const TableTennisPlayer & tp);
    unsigned int Rating() const { return rating; }
    void ResetRating (unsigned int r) {rating = r;}
};

#endif

1.2.2 table-tennis base class mothods

//tabtenn1.cpp -- simple base-class methods
#include "tabtenn1.h"
#include 

TableTennisPlayer::TableTennisPlayer (const string & fn, 
    const string & ln, bool ht) : firstname(fn),
       lastname(ln), hasTable(ht) {}
    
void TableTennisPlayer::Name() const
{
    std::cout << lastname << ", " << firstname;
}

// RatedPlayer methods
RatedPlayer::RatedPlayer(unsigned int r, const string & fn,
     const string & ln, bool ht) : TableTennisPlayer(fn, ln, ht)
{
    rating = r;
}

RatedPlayer::RatedPlayer(unsigned int r, const TableTennisPlayer & tp)
    : TableTennisPlayer(tp), rating(r)
{
}

1.2.3 using base class and derived class

// usett1.cpp -- using base class and derived class
#include 
#include "tabtenn1.h"

int main ( void )
{
    using std::cout;
    using std::endl;
    TableTennisPlayer player1("Tara", "Boomdea", false);
    RatedPlayer rplayer1(1140, "Mallory", "Duck", true);
    rplayer1.Name();          // derived object uses base method
    if (rplayer1.HasTable())
        cout << ": has a table.\n";
    else
        cout << ": hasn't a table.\n";
    player1.Name();           // base object uses base method
    if (player1.HasTable())
        cout << ": has a table";
    else
        cout << ": hasn't a table.\n";
    cout << "Name: ";
    rplayer1.Name();
    cout << "; Rating: " << rplayer1.Rating() << endl;
// initialize RatedPlayer using TableTennisPlayer object
    RatedPlayer rplayer2(1212, player1);
    cout << "Name: ";
    rplayer2.Name();
    cout << "; Rating: " << rplayer2.Rating() << endl;
    // std::cin.get();
    return 0;
}

the output of the program：

Duck, Mallory: has a table.
Boomdea, Tara: hasn't a table.
Name: Duck, Mallory; Rating: 1140
Name: Boomdea, Tara; Rating: 1212

1.3 Polymorphism

Polymorphism means “many shapes.” It refers to the ability of one object to have many types.

you can encounter situations in which you want a method to behave differently for the derived class than it does for the base class！！

1.2.1 bank account classes

// brass.h  -- bank account classes
#ifndef BRASS_H_
#define BRASS_H_
#include 
// Brass Account Class
class Brass
{
private:
    std::string fullName;
    long acctNum;//Account numbe
    double balance;//Current balance
public:
    Brass(const std::string & s = "Nullbody", long an = -1,
                double bal = 0.0);
    void Deposit(double amt);
    virtual void Withdraw(double amt);
    double Balance() const;
    virtual void ViewAcct() const;
    virtual ~Brass() {}
};

//Brass Plus Account Class
class BrassPlus : public Brass
{
private:
    double maxLoan;//An upper limit to the overdraft protection
    double rate;//An interest rate charged for overdraft loans
    double owesBank;//The overdraft amount currently owed to the bank
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

• Both the Brass class and the BrassPlus class declare the ViewAcct() and Withdraw() methods; these are the methods that will behave differently for a BrassPlus object than they do with a Brass object.

• The Brass class uses the new keyword virtual in declaring ViewAcct() and Withdraw().These methods are now termed virtual methods.

1.2.2 bank account class methods

// brass.cpp -- bank account class methods
#include 
#include "brass.h"
using std::cout;
using std::endl;
using std::string;

// 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;
}

void Brass::Deposit(double amt)
{
    if (amt < 0)
        cout << "Negative deposit not allowed; "
             << "deposit is cancelled.\n";
    else
        balance += amt;
}

void Brass::Withdraw(double amt)
{
    // set up ###.## format
    format initialState = setFormat();
    precis prec = cout.precision(2);

    if (amt < 0)
        cout << "Withdrawal amount must be positive; "

             << "withdrawal canceled.\n";
    else if (amt <= balance)
        balance -= amt;
    else
        cout << "Withdrawal amount 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); // Restore original format
}

// BrassPlus Methods
BrassPlus::BrassPlus(const string & s, long an, double bal,
           double ml, double r) : Brass(s, an, bal)
{
    maxLoan = ml;
    owesBank = 0.0;
    rate = r;
}

BrassPlus::BrassPlus(const Brass & ba, double ml, double r)
           : Brass(ba)   // uses implicit copy constructor
{
    maxLoan = ml;
    owesBank = 0.0;
    rate = r;
}

// redefine how ViewAcct() works
void BrassPlus::ViewAcct() const
{
    // set up ###.## format
    format initialState = setFormat();
    precis prec = cout.precision(2);

    Brass::ViewAcct();   // display base portion
    cout << "Maximum loan: $" << maxLoan << endl;
    cout << "Owed to bank: $" << owesBank << endl;
    cout.precision(3);  // ###.### format
    cout << "Loan Rate: " << 100 * rate << "%\n";
    restore(initialState, prec); 
}

// redefine how Withdraw() works
void BrassPlus::Withdraw(double amt)
{
    // set up ###.## format
    format initialState = setFormat();
    precis prec = cout.precision(2);

    double bal = Balance();
    if (amt <= bal)
        Brass::Withdraw(amt);
    else if ( amt <= bal + maxLoan - owesBank)
    {
        double advance = amt - bal;
        owesBank += advance * (1.0 + rate);
        cout << "Bank advance: $" << advance << endl;
        cout << "Finance charge: $" << advance * rate << endl;
        Deposit(advance);
        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);
}

1.2.3 Using the Brass and BrassPlus Classes

// usebrass2.cpp -- polymorphic example
// compile with brass.cpp
#include 
#include 
#include "brass.h"
const int CLIENTS = 4;

int main()
{
   using std::cin;
   using std::cout;
   using std::endl;

   Brass * p_clients[CLIENTS];
   std::string temp;
   long tempnum;
   double tempbal;
   char kind;

   for (int i = 0; i < CLIENTS; i++)
   {
       cout << "Enter client's name: ";
       getline(cin,temp);
       cout << "Enter client's account number: ";
       cin >> tempnum;
       cout << "Enter opening balance: $";
       cin >> tempbal;
       cout << "Enter 1 for Brass Account or "
            << "2 for BrassPlus Account: ";
       while (cin >> kind && (kind != '1' && kind != '2'))
           cout <<"Enter either 1 or 2: ";
       if (kind == '1')
           p_clients[i] = new Brass(temp, tempnum, tempbal);
       else
       {
           double tmax, trate;
           cout << "Enter the overdraft limit: $";
           cin >> tmax;
           cout << "Enter the interest rate "
                << "as a decimal fraction: ";
           cin >> trate;
           p_clients[i] = new BrassPlus(temp, tempnum, tempbal,
                                        tmax, trate);
        }
        while (cin.get() != '\n')
            continue;
   }
   cout << endl;
   for (int i = 0; i < CLIENTS; i++)
   {
       p_clients[i]->ViewAcct();
       cout << endl;
   }
              
   for (int i = 0; i < CLIENTS; i++)
   {
       delete p_clients[i];  // free memory
   }
   cout << "Done.\n";         
 /* code to keep window open 
   if (!cin)
      cin.clear();
   while (cin.get() != '\n')
      continue;
*/
   return 0; 
}

2 abstract base classes

You’ve seen simple inheritance and the more intricate polymorphic inheritance. The next step in increasing sophistication is the abstract base class (ABC).

1.2.1 bank account classes

// acctabc.h -- bank account classes
#ifndef ACCTABC_H_
#define ACCTABC_H_
#include 
#include 
// Abstract Base Class
class AcctABC
{
private:
    std::string fullName;
    long acctNum;
    double balance;

protected:
    struct Formatting
    {
        std::ios_base::fmtflags flag;
        std::streamsize pr;
    };


    const std::string & FullName() const {return fullName;}
    long AcctNum() const {return acctNum;}
    Formatting SetFormat() const;
    void Restore(Formatting & f) const;

public:
    AcctABC(const std::string & s = "Nullbody", long an = -1,double bal = 0.0);
    void Deposit(double amt) ;
    virtual void Withdraw(double amt) = 0; // pure virtual function
    double Balance() const {return balance;};
    virtual void ViewAcct() const = 0; // pure virtual function
    virtual ~AcctABC() {}
};



// Brass Account Class
class Brass :public AcctABC
{
public:
    Brass(const std::string & s = "Nullbody", long an = -1,double bal = 0.0) : AcctABC(s, an, bal) { }
    virtual void Withdraw(double amt);
    virtual void ViewAcct() const;
    virtual ~Brass() {}
};


//Brass Plus Account Class
class BrassPlus : public AcctABC
{
private:
    double maxLoan;
    double rate;
    double owesBank;

public:
    BrassPlus(const std::string & s = "Nullbody", long an = -1,double bal = 0.0, double ml = 500,double r = 0.10);
    BrassPlus(const Brass & ba, double ml = 500, double r = 0.1);
    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

1.2.2 bank account class methods

// acctabc.cpp -- bank account class methods
#include 
#include "acctabc.h"
using std::cout;
using std::ios_base;
using std::endl;
using std::string;

// Abstract Base Class
AcctABC::AcctABC(const string & s, long an, double bal)
{
    fullName = s;
    acctNum = an;
    balance = bal;
}

void AcctABC::Deposit(double amt)
{
    if (amt < 0)
        cout << "Negative deposit not allowed; "
             << "deposit is cancelled.\n";
    else
        balance += amt;
}

void AcctABC::Withdraw(double amt)
{
    balance -= amt;
}

// protected methods for formatting
AcctABC::Formatting AcctABC::SetFormat() const
{
 // set up ###.## format
    Formatting f;
    f.flag = 
        cout.setf(ios_base::fixed, ios_base::floatfield);
    f.pr = cout.precision(2);
    return f; 
}

void AcctABC::Restore(Formatting & f) const
{
    cout.setf(f.flag, ios_base::floatfield);
    cout.precision(f.pr);
}

// Brass methods
void Brass::Withdraw(double amt)
{
    if (amt < 0)
        cout << "Withdrawal amount must be positive; "
             << "withdrawal canceled.\n";
    else if (amt <= Balance())
        AcctABC::Withdraw(amt);
    else
        cout << "Withdrawal amount of $" << amt
             << " exceeds your balance.\n"
             << "Withdrawal canceled.\n";
}

void Brass::ViewAcct() const
{
   
    Formatting f = SetFormat();
    cout << "Brass Client: " << FullName() << endl;
    cout << "Account Number: " << AcctNum() << endl;
    cout << "Balance: $" << Balance() << endl;
    Restore(f);
}

// BrassPlus Methods
BrassPlus::BrassPlus(const string & s, long an, double bal,
           double ml, double r) : AcctABC(s, an, bal)
{
    maxLoan = ml;
    owesBank = 0.0;
    rate = r; 
}

BrassPlus::BrassPlus(const Brass & ba, double ml, double r)
           : AcctABC(ba)   // uses implicit copy constructor
{
    maxLoan = ml;
    owesBank = 0.0;
    rate = r;
}

void BrassPlus::ViewAcct() const
{
    Formatting f = SetFormat();

    cout << "BrassPlus Client: " << FullName() << endl;
    cout << "Account Number: " << AcctNum() << endl;
    cout << "Balance: $" << Balance() << endl;
    cout << "Maximum loan: $" << maxLoan << endl;
    cout << "Owed to bank: $" << owesBank << endl;
    cout.precision(3);
    cout << "Loan Rate: " << 100 * rate << "%\n";
    Restore(f);
}

void BrassPlus::Withdraw(double amt)
{
    Formatting f = SetFormat();

    double bal = Balance();
    if (amt <= bal)
        AcctABC::Withdraw(amt);
    else if ( amt <= bal + maxLoan - owesBank)
    {
        double advance = amt - bal;
        owesBank += advance * (1.0 + rate);
        cout << "Bank advance: $" << advance << endl;
        cout << "Finance charge: $" << advance * rate << endl;
        Deposit(advance);
        AcctABC::Withdraw(amt);
    }
    else
        cout << "Credit limit exceeded. Transaction cancelled.\n";
    Restore(f); 
}

1.2.3 using an abstract base class

// usebrass3.cpp -- polymorphic example
// compile with acctacb.cpp
#include 
#include 
#include "acctabc.h"
const int CLIENTS = 4;

int main()
{
   using std::cin;
   using std::cout;
   using std::endl;

   AcctABC * p_clients[CLIENTS];
   std::string temp;
   long tempnum;
   double tempbal;
   char kind;

   for (int i = 0; i < CLIENTS; i++)
   {
       cout << "Enter client's name: ";
       getline(cin,temp);
       cout << "Enter client's account number: ";
       cin >> tempnum;
       cout << "Enter opening balance: $";
       cin >> tempbal;
       cout << "Enter 1 for Brass Account or "
            << "2 for BrassPlus Account: ";
       while (cin >> kind && (kind != '1' && kind != '2'))
           cout <<"Enter either 1 or 2: ";
       if (kind == '1')
           p_clients[i] = new Brass(temp, tempnum, tempbal);
       else
       {
           double tmax, trate;
           cout << "Enter the overdraft limit: $";
           cin >> tmax;
           cout << "Enter the interest rate "
                << "as a decimal fraction: ";
           cin >> trate;
           p_clients[i] = new BrassPlus(temp, tempnum, tempbal,
                                        tmax, trate);
        }
        while (cin.get() != '\n')
            continue;
   }
   cout << endl;
   for (int i = 0; i < CLIENTS; i++)
   {
       p_clients[i]->ViewAcct();
       cout << endl;
   }
              
   for (int i = 0; i < CLIENTS; i++)
   {
       delete p_clients[i];  // free memory
   }
   cout << "Done.\n";    
   // cin.get();
   return 0; 
}