Lab #5 - Inheritance and Over-Riding
Question 1 - Company Hierarchy
In a Company Hierarchy consisting of Clerk, Manager and Director, the invoice approval limits are as follows:-
- Clerk - $100
- Manager - $500
- Director - $1000
The UML Class Diagram for the Clerk is as shown.
| Clerk | |
| - | name : String |
| - | designation: String |
| * | getName : String |
| * | getDesignation : String |
| * | introduce() : String |
| * | approveInvoice(in invoiceAmount:double) : boolean |
- Depict the Company Hierarchy in a UML Class Diagram.
- Implement the Company Hierarchy. Over-Ride the approveInvoice function to ensure the approval limits are adhered to. [Hint: create the main() loop in the Director class and create instances of Clerk, Manager and Director]
Solution:
#include <iostream>
/**
* @brief Class Clerk
*/
class Clerk
{
private:
std::string name, designation;
public:
Clerk(std::string);
Clerk(std::string, std::string);
~Clerk();
std::string getName();
std::string getDesignation();
std::string introduce();
bool approveInvoice(double);
};
Clerk::Clerk(std::string name)
{
this->name = name;
this->designation = "Clerk";
}
Clerk::Clerk(std::string name, std::string designation)
{
this->name = name;
this->designation = designation;
}
Clerk::~Clerk()
{
}
std::string Clerk::getName()
{
return this->name;
}
std::string Clerk::getDesignation()
{
return this->designation;
}
std::string Clerk::introduce()
{
return "My name is " + this->name + " and I am a " + this->designation;
}
bool Clerk::approveInvoice(double amount)
{
if (amount <= 100)
return true;
else
return false;
}
/**
* @brief Class Manager
*/
class Manager : public Clerk
{
private:
public:
Manager(std::string);
Manager(std::string, std::string);
~Manager();
bool approveInvoice(double);
};
Manager::Manager(std::string name) : Clerk(name, "Manager")
{
}
Manager::Manager(std::string name, std::string designation) : Clerk(name, designation)
{
}
Manager::~Manager()
{
}
bool Manager::approveInvoice(double amount)
{
if (amount <= 500)
return true;
else
return false;
}
/**
* @brief Class Manager
*/
class Director : public Manager
{
private:
public:
Director(std::string);
~Director();
bool approveInvoice(double);
};
Director::Director(std::string name) : Manager(name, "Director")
{
}
Director::~Director()
{
}
bool Director::approveInvoice(double amount)
{
if (amount <= 1000)
return true;
else
return false;
}
// program 1
int main(int argc, char const *argv[])
{
Clerk clerk("John");
Manager manager("Jane");
Director director("Jack");
std::cout << clerk.introduce() << std::endl;
std::cout << manager.introduce() << std::endl;
std::cout << director.introduce() << std::endl;
std::cout << (clerk.approveInvoice(77) ? "True" : "False") << std::endl;
std::cout << (clerk.approveInvoice(100) ? "True" : "False") << std::endl;
std::cout << (clerk.approveInvoice(124) ? "True" : "False") << std::endl;
std::cout << (manager.approveInvoice(427) ? "True" : "False") << std::endl;
std::cout << (manager.approveInvoice(500) ? "True" : "False") << std::endl;
std::cout << (manager.approveInvoice(584) ? "True" : "False") << std::endl;
std::cout << (director.approveInvoice(927) ? "True" : "False") << std::endl;
std::cout << (director.approveInvoice(1000) ? "True" : "False") << std::endl;
std::cout << (director.approveInvoice(1084) ? "True" : "False") << std::endl;
return 0;
}
Output:
My name is John and I am a Clerk
My name is Jane and I am a Manager
My name is Jack and I am a Director
True
True
False
True
True
False
True
True
False
Question 2 - Company Hierarchy with Outsourcing
To cut costs, the Company decided to take on Contractors.
A Contractor has a Name in the company records, but has no formal designation. A Contractor cannot approveInvoice (but of course!).
Suppose that at a Company function, everyone has to introduce himself / herself:-
Hello, my name is xxx. My designation is XXX.
or
Hello, my name is yyy. I am a Contractor.
- Design the new Company Hierarchy in a UML Class Diagram, to accommodate the Contractor. [Hint: pull up the common attributes / properties and behaviour into an Abstract Class.]
- Implement the new Company Hierarchy. Keep the main() loop in the Director class.
Solution:
...
// program 2
class Contractor : protected Clerk
{
private:
public:
Contractor(std::string);
~Contractor();
std::string introduce();
std::string getName();
};
Contractor::Contractor(std::string name) : Clerk(name)
{
}
Contractor::~Contractor()
{
}
std::string Contractor::introduce()
{
return "My name is " + this->getName() + " and I am a Contractor";
}
std::string Contractor::getName()
{
return Clerk::getName();
}
int main(int argc, char const *argv[])
{
Contractor contractor("John");
std::cout << contractor.introduce() << std::endl;
std::cout << contractor.getName() << std::endl;
return 0;
}
My name is John and I am a Contractor
John
Question 3 - Fraud!
Suppose a Director in the Company tries to impersonate his Clerk at the Company function by introducing himself as a Clerk. By using casting, show how that this is possible.
Clerk* cPtr = new Manager(...);
cPtr->introduce();
Suppose a Clerk in the Company tries to impersonate his Manager at the Company function. Explain why this is not possible.
Manager* mPtr = new Clerk(...);
mPtr->introduce();
Solution:
...
// program 3
int main(int argc, char const *argv[])
{
Clerk *cPtr = new Manager("John");
std::cout << cPtr->introduce() << std::endl;
try
{
Manager *mPtr = new Clerk("Jane");
mPtr->introduce();
}
catch (const std::exception &e)
{
std::cerr << e.what() << 'n';
}
return 0;
}
My name is John and I am a Manager