1. Inheritance
Types of inheritance
Implementing inheritance
Interface

2. TYPES OF INHERITANCE
 Implementation inheritance means that a
type derives from a base type, taking all the
base type’s member fields and functions.
 Interface inheritance means that a type
inherits only the signatures of the functions
and does not inherit any implementations.

3. IMPLEMENTATION
INHERITANCE
 A class derive from another class
syntax:
Class MyDerivedClass: MyBaseClass
{ //function and data memebers here}
 A class derive from interface,the list of base class
and interfaces is separated by commas
syntax:
Public class MyDerivedClass: MyBaseClass,
Interface1,Interface2
{//function and data memebers here}

4. VIRTUAL METHODS
 By declaring a base class function as virtual, you allow the function to
be overridden in any derived classes.
Class MyBaseClass
{
public virtual string VirtualMethod( )
{ return “this method is virtural and defined in MyBaseClass” ;}
}
 It is also permitted to declare a property as virtual.
Public virtual string ForeName
{
get { return foreName;}
set { foreName=value;}
}

5. HIDING METHODS
 If a method with the same signature is declared in both base and derived
classes, but the methods are not declared as virtual and override,
respectively, then the derived class version is said to hide the base class
version.
 Abstract classes and Functions:
 An abstract class cannot be instantiated,were as an abstract function does
not have an implementation,and must be overriden in any non-abstract
derived class
 Abstract function is automatically virtual.

6. SEALED CLASSES AND
METHODS
 C# allows classes and methods to be declared as sealed.
 In case of class this means that you can’t inherit from that class
syntax:
sealed class Class_Name
{ // etc }
 In case of method
syntax:
class MyClass: MyclassBase
{
public sealed override void FinalMethod()
{ // etc }
}
class DerivedClass: MyClass
{
public override void FinalMethod() // wrong..will give compilation error
{ // etc } }

7. Constructors of Derived Classes
 Adding a constructor in a Hierarchy
 Adding a constructor with parameters to a
Hierarchy

8. MODIFIERS
 Modifiers can indicate the visibility of a methods.
MODIFIER APPLIES TO DESCRIPTION
public Any type or members The item is visible to any
other code.
protected Any member of a type, also The item is visible only to
any nested type any derived type.
internal Any member of a type, also The item is visible only with
any nested type in its containing assembley.
private Any types or memebers The item is visible only
inside the type to which it
belongs
protected internal Any member of a type, also The item is visible to any
any nested type code within its containing
assembly and also to any
code inside a derived type

9. MODIFIER APPLIES TO DESCRIPTION
new Function members The member hides an inherited
member with the same signature
static All members The member does not operate on a
specific instance of the class
virtual Function members only The member can be overridden by a
derived class
abstract Function members only A virtual member that defines the
signature of the member, but doesn’t
provide an implementation.
override Function members only The member overrides an inherited
virtual or abstract member
sealed Classes, methods, and class cannot be inherited, member
properties overrides an inherited virtual member,
but cannot be overridden by any
members in any derived classes
extern static [DllImport] The member is implemented
methods only externally, in a different language.

10. INTERFACES
syntax:
public interface Interface_Name
{
void method();
}
 You can never instantiate an interface, it contains only the
signatures of its members.
 An interface has neither constructors nor fields and also not
allowed to contain operator overloads.
 An interface members are always implicitly public, and cannot
be declared as virtual or static.