The document discusses inheritance, polymorphism, properties, interfaces, and multiple inheritance in C#. It provides code examples to demonstrate: 1. Defining base and derived classes to represent employees with inheritance. 2. Using a constructor in a derived class to call the base class constructor. 3. Polymorphism through overriding virtual methods in derived classes. 4. Using properties with getters and setters instead of public fields. 5. Implementing multiple interfaces on a class and explicitly implementing interface members. 6. Issues with multiple inheritance with classes and how interfaces can allow for multiple inheritance.

1. 21. Inheritance in c#
using System;
public class Employee
{
public string FirstName;
public string LastName;
public string Email;
public void FullNamePrint()
{
Console.WriteLine("Name = {0} {1}", FirstName, LastName);
}
}
public class FullTimeEmployee : Employee
{
public float AnnualSalary;
public void Salary()
{
Console.WriteLine("Salary = {0}", AnnualSalary);
}
}
public class PartTimeEmployee : Employee
{
public float Hourlysalary;
}
class Program
{
public static void Main()
{
FullTimeEmployee FTE = new FullTimeEmployee();
FTE.FirstName = "Gourav";
FTE.LastName = "Pant";
FTE.Email = "gourav.pant375@gmail.com";
FTE.AnnualSalary = 2000;
FTE.FullNamePrint();
FTE.Salary();
PartTimeEmployee PTE = new PartTimeEmployee();
PTE.FirstName = "Shrawan";
PTE.LastName = "Chowbey";

2. PTE.Hourlysalary = 300;
PTE.FullNamePrint();
}
}
21. Inheritance in c#
using System;
class ParentClass
{
public ParentClass()
{
Console.WriteLine("Parent Constructor Called");
}
public ParentClass(string Message)
{
Console.WriteLine(Message);
}
}
class ChildClass : ParentClass //Single level Inheritence
{
public ChildClass() : base("Hello this is another Constructor") //base() method is
use to choose which constructor is called from Parent Class
{
Console.WriteLine("Child Constructor Called");
}
}
class Program
{
public static void Main()
{
ChildClass CC = new ChildClass(); //Parent Class constructor call first before
child class constructor
}
}
23. Polymorphism in C#

3. using System;
public class Employee
{
public string FirstName = "Gourav";
public string LastName = "Pant";
public virtual void PrintFullName()
{
Console.WriteLine(FirstName + " " + LastName);
}
}
public class PartTimeEmployee : Employee
{
public override void PrintFullName()
{
Console.WriteLine(FirstName + " " + LastName + "- PART TIME");
}
}
public class FullTimeEmployee : Employee
{
public override void PrintFullName()
{
Console.WriteLine(FirstName + " " + LastName + "- FULL TIME");
}
}
public class TemporaryEmployee : Employee //if override function is not there then
virtual funtion is used.
{
//public override void PrintFullName()
//{
// Console.WriteLine(FirstName + " " + LastName + "- TEMPORARY");
//}
}
class Program
{
public static void Main()
{
Employee E1 = new Employee();
E1.PrintFullName();
Employee E2 = new PartTimeEmployee(); // By the help of Parent Class Ref
variable(E2) we can invoke PartTimeEmployee print function during runtime.
E2.PrintFullName();
Employee E3 = new FullTimeEmployee();
E3.PrintFullName();
Employee E4 = new TemporaryEmployee();
E4.PrintFullName();
}

4. }
26. Why Properties used and use of Getter and Setter methods in C#
using System;
public class Student
{
private int _id;
private string _name;
private int _passMark = 57;
public void SetId(int ID)
{
if (ID <= 0)
{
throw new Exception("Id cannot be less than equal to zero");
}
this._id = ID;
}
public int GetId()
{
return this._id;
}
public void SetName(string Name)
{
if (string.IsNullOrEmpty(Name)) //IsNullOrEmpty is a method of string
class used to check the value is null or empty
{
throw new Exception("Name cannot be Blank or null");
}
this._name = Name;
}
public string GetName()
{
return string.IsNullOrEmpty(this._name) ? "No Name" : this._name; //Ternary
Operator used instead of if else
}
public int GetPassMark()
{
return this._passMark;
}
}
public class Program
{

5. public static void Main()
{
Student S = new Student();
S.SetId(5);
Console.WriteLine("Id = {0}",S.GetId());
//S.SetName("Gourav"); SetName method is missing so "No Name" should be
return
S.SetName("Gourav");
Console.WriteLine("Name = {0}", S.GetName());
Console.WriteLine("PassMark = {0}", S.GetPassMark()); //PassMark field
should be read only
}
}
27. Properties in C#
using System;
public class Student
{
private int _id;
private string _name;
private int _passMark = 33;
public int ID
{
set
{
if (value <= 0)
{
throw new Exception("Student Id cannot be less than or equal to zero");
}
this._id = value;
}
get
{
return this._id;
}
}
public string Name
{
set
{
if (string.IsNullOrEmpty(value))
{
throw new Exception("Name cannot be Blank or null");
}

6. this._name = value;
}
get
{
return string.IsNullOrEmpty(this._name) ? "No Name" : this._name;
}
}
public int PassMark
{
get
{
return this._passMark;
}
}
}
public class Program
{
public static void Main()
{
Student C1 = new Student();
C1.ID = 101;
C1.Name = "Gourav"; //Name is missing so "No Name" should be return
Console.WriteLine("Id = {0}", C1.ID);
Console.WriteLine("Name = {0}", C1.Name);
Console.WriteLine("PassMark = {0}", C1.PassMark); //PassMark field
should be read only
}
}
30. Interfaces in C#
using System;
interface Icustomer1
{
void Print1();
}
interface Icustomer2 : Icustomer1 // Icustomer2 Interface inherits from Icustomer1
Interface
{
void Print2();
}

7. public class Customer : Icustomer2 // Customer Class has to implement the both
interfaces members
{
public void Print1()
{
Console.WriteLine("Print1 Method");
}
public void Print2()
{
Console.WriteLine("Print2 Method");
}
}
public class Program
{
public static void Main()
{
Icustomer2 C1 = new Customer();
C1.Print1();
C1.Print2();
}
}
31. Explicit interfaces implementation
using System;
interface I1
{
void InterfaceMethod();
}
interface I2
{
void InterfaceMethod();
}
public class Program : I1, I2
{
void I1.InterfaceMethod()
{
Console.WriteLine("I1 Interface Method");
}

8. void I2.InterfaceMethod()
{
Console.WriteLine("I2 Interface Method");
}
public static void Main()
{
/* Program P = new Program();
((I1)P).InterfaceMethod(); // 2 Methods to do explicit interface
implementation. This is typecast method.
((I2)P).InterfaceMethod(); */
I1 i1 = new Program();
i1.InterfaceMethod();
I2 i2 = new Program();
i2.InterfaceMethod();
}
}
Default & Explicit Implementation:-
using System;
interface I1
{
void InterfaceMethod();
}
interface I2
{
void InterfaceMethod();
}
public class Program : I1, I2
{
public void InterfaceMethod() // Implement this method is default
{
Console.WriteLine("I1 Interface Method");
}
void I2.InterfaceMethod() // Implement this method is Explicit
{
Console.WriteLine("I2 Interface Method");
}
public static void Main()
{

9. Program P = new Program();
P.InterfaceMethod(); // Call the default InterfaceMethod()
((I2)P).InterfaceMethod(); // Call the Explicit InterfaceMethod() which is
of I2 Interface method
}
}
34. Problems of multiple class inheritance
using System;
class A
{
public virtual void print()
{
Console.WriteLine("A Implementation");
}
}
class B : A
{
public override void print()
{
Console.WriteLine("B Implementation");
}
}
class C : A
{
public override void print()
{
Console.WriteLine("C Implementation");
}
}
class D : B, C
{
}
public class Program
{
public static void Main()
{
D d = new D();
d.print(); // So confusion is that which print method should be invoke from
both B and C
}
}

10. 35. Multiple class inheritance using interfaces
using System;
interface IA
{
void AMethod();
}
class A : IA
{
public void AMethod()
{
Console.WriteLine("A Method");
}
}
interface IB
{
void BMethod();
}
class B : IB
{
public void BMethod()
{
Console.WriteLine("B Method");
}
}
class AB : IA, IB
{
A a = new A();
B b = new B();
public void AMethod()
{
a.AMethod();
}
public void BMethod()
{
b.BMethod();
}
}
public class Program
{
public static void Main()
{
AB ab = new AB();
ab.AMethod();
ab.BMethod();
}
}