The document explains the concepts of abstract classes and interfaces in object-oriented programming. Abstract classes are used to define a base class with shared functionality that cannot be instantiated directly, while interfaces serve as blueprints for classes without containing implementation details. It includes example code to demonstrate how to implement abstract methods and interface methods in derived classes.

1. Abstract classes &
Interfaces

2. Abstract Classes
• Process to hide internal details
• Showing only their functionality
• The keyword abstract is used to create abstract classes
• Abstract class must contain at least one abstract method in it

3. Abstract Classes
• Use abstract classes at the time of inheritance
• Abstract classes cannot be inherited by structures
• It contains constructors and destructors
• Cannot support multiple inheritance

4. Abstract Classes
• It can have both abstract and non abstract methods
• It cannot be instantiated
• Implementation must be provided by derived classes
• derived class is forced to provide the implementation of all the abstract
methods.

5. Abstract Classes
• Syntax
• <Access Specifier> abstract class <class Name>{
// abstract method
}

6. Abstract Methods

7. Abstract Methods
• Abstract classes that contain one or more abstract methods
• Method which is declared abstract
• Abstract method has no body
• Abstract methods only be declare inside the abstract class only

8. Abstract Methods
• Abstract keyword is used to create abstract methods
• Abstract classes have at least one abstract method
• Implementation is done by a derive class
• Use override keyword to implement the abstract method in derive class
• It is override in non abstract classes

9. Abstract Methods
• Cannot be use private access specifier
• Use only public and protected access specifier
• Abstract methods cannot be static
• Syntax
<Access specifier> abstract <data type> <method name> ( );

10. Program
• using System;
• public abstract class Shape
• {
• public abstract void draw();
• }
• public class Rectangle : Shape
• {
• public override void draw()
• {
• Console.WriteLine("drawing rectangle...");
• }
• }
• public class Circle : Shape {
• public override void draw() {
• Console.WriteLine("drawing circle..."); }
• }
• public class TestAbstract {
• public static void Main() {
• Shape s;
• s = new Rectangle();
• s.draw();
• s = new Circle();
• s.draw();
• } }

11. Interfaces

12. Interface
• blueprint of class
• can have methods, properties, events, and indexers as its members
• Cannot contain constructor
• Interface cannot be instantiated

13. Interface
• Cannot have private member
• All members in interface is public by default
• All methods in interface are abstract methods
• Cannot have a method body
• Implementation is done in derive class

14. Interface
• Override all of its members in derive class
• Used to achieve Multiple Inheritance
• Multiple interface is separated by comma
• interface keyword is used to create interface

15. Syntax
• <Access Specifier> interface <Name>{
}

16. Program
• using System;
• public interface Drawable
• {
• void draw();
• }
• public class Rectangle : Drawable
• {
• public void draw()
• {
• Console.WriteLine("drawing rectangle...");
• }
• }
• public class Circle : Drawable {
• public void draw() {
• Console.WriteLine("drawing circle...");
• } }
• public class TestInterface {
• public static void Main() {
• Drawable d;
• d = new Rectangle();
• d.draw();
• d = new Circle();
• d.draw();
• }
• }