What is an abstract class in c#

What is an abstract class?  

•  An abstract class can contain abstract and non-abstract member.
•  An abstract class can be used as a base class 
•  An abstract method does not have body/definition.
•  An abstract class cannot be marked as a sealed class.
•  We can not create an object of abstract class.
•  We can create abstract class and method by using "abstract" keyword.
•  We can not provide the static keyword to the abstract method.
•  Once we inherit an abstract class in derived class then we must provide definition to the abstract member.
• We can implement the abstract method by using “override” keyword.

  

Syntax: Creating abstract class.

<modifier> abstract class <class_name>

{

// member

}

Syntax:  Creating the abstract method.

<modifier> abstract return_type <method_name>(<parameter_list>);

Example: Simple example to understand the basic concept of abstract class and abstract method.

using System;

namespace AbstractClassProject

{

    public abstract class DiscountedCustomer

    {

        public int CustId { get; set; }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public int Price { get; set; }

        public int Discount { get; set; }

        

        public string GetCustomer() // Non Abstract Method

        {

            return this.FirstName + " " + this.LastName;

        }

        public abstract int CalculateDiscount(); // Abstract Method       

    }

    public class Customer:DiscountedCustomer

    {        

        public override int CalculateDiscount()

        {

            return this.Price * this.Discount/100;

        }

    }

    class Program

    {

        static void Main(string[] args)

        {

            Customer customer = new Customer() {

                CustId=101,

                FirstName="Mauli",

                LastName ="Gadewar",

                 Price = 500,

                 Discount =20

            };

            Console.WriteLine("Customer Full Name is {0}", customer.GetCustomer());

            Console.WriteLine("Total Price is {0}", customer.Price);

            Console.WriteLine("Customer Discount Rs is {0} ", customer.CalculateDiscount());

            Console.ReadLine();

        }

    }

}

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Constant Vs Readonly In C#

Difference between constant and readonly in C#

1. constant:

•  It is used to store the constant value.
•  It is compiled time constant.
•  We can not modify/change the constant value.
•  The Constant variable can by access by using the class name.
•  We must assign the value to the constant variable at the declaration time.
•  We can not provide the static keyword to the constant variable.
•  We can not access the constant variable by using object of the class.

2. Readonly keyword:

•  It is used to store the constant value.
•  It is run time constant.
•  We can modify/change the readonly variable value in the constructor of the class.
•  The readonly variable can be accessed by using object of the class or class name.
•  we can provide the static keyword to the readonly variable.
•  We can access the readonly variable by using object of the class or class name.

Example: 

using System;

namespace CSharpProject

{

    class Program

    {

        public const string strConnection = "Test Connection";

        //public static readonly double Pi = 3.1; // we can define static keyword to the readonly variables

        public  readonly double Pi = 3.1;

        public Program()

        {

            Pi = 3.14;

        }               

        static void Main(string[] args)

        {

            Program pro = new Program();

            Console.WriteLine(pro.Pi); // Calling not static readonly variable by using object of class.

           // Console.WriteLine(Program.Pi);// calling static readonly keyword by using class name.

            Console.WriteLine(Program.strConnection);

            Console.ReadLine();

        }

    }

}

More Details watch the following video on the same:

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About Me

Shrimant Telgave is a Software Developer, Author, Blogger having experience in Design, developing and maintaining large-scale applications. He is a technology aggressive and blogs on his own website www.programmingwithshri.com as well as www.c-sharpcorner.com

He has a good experience in C#, ASP.NET, ASP.NET MVC, SQL Server, Web Services, WCF, Entity Framework, LINQ, ADO.NET, JavaScript, jQuery. He did his master degree from Pune University. He did Microsoft .NET training from Hyderabad. 

He keeps an eye on new technologies and implements them. Use the best way and optimized approaches to solving the problem, issues and ease the process by using well equipped and standard techniques to boost the performance of the applications.

You can find out me on following links:

• www.c-sharpcorner.com

• www.quora.com

• www.youtube.com

• https://twitter.com/shrimant_vt

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C#.NET Tutorials [step by step]

• What is Data Abstraction and Encapsulation with example?

• What is Polymorphism in C# ? Compile time and Runtime polymorphism in C# ?

• What is Interface in C# [Step by Step] ? Why should we use Interface In C# ?

• What is Implicit Interface And Explicit Interface In C# With Example[Step by Step]

• What is Delegate in C# ? Singlecast and Multicast Delegates with example

• Difference Between Constant Vs Readonly In C#

• Abstract Class with Example
• What is Diamond Problem in C#

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[C#] - What is Delegates in C# Example | Use of Delegates in C# | Type of Delegates in C#

In this article, we will learn Delegate in C#.NET with example, Type of delegate in c#  [real time] example and Anonymous method. I will explain Singlecast Delegate and Multicast Delegate in c#.net with an example [step by step].

What is the Delegate?

It is type safe function pointer. Which hold the reference/address of the method.

Type safe function means

1. The return type of delegate should be the same as the return type of method.

2. The parameter type of delegate should be the same as the parameter type of method.

In order to work with the delegate, we have to follow three steps as follow.

Step-1: Define a Delegate.

[<modifier>] delegate void|type(return_type) <delegate_name>([<parameter list>]);

e.g:

1. public delegate void MessageDelegate()

Step-2: Instantiating the delegate or binding method to the delegate instance.

<delegate_name> object_name = new <delegate_name>(<method_name>);

OR

<delegate_name> object_name = <method_name>;

e.g:

1. // Step-2: Instantiating the Delegate.
2. MessageDelegate message = new MessageDelegate(Email.DisplayMessage);

Note: <method_name> If the method is static then, We call by using the class name. If the method is non-static then we can call that method by using object of the class.

There is two way to instantiating the delegate as mentioned above. I will go through one by one in the example so that you can understand better.

Step-3: Invoking the delegate.

<delegate_object>.Invoke(<parameters>);

OR

<delegate_object>(<parameters>);

e.g: 

1. // Step-3: Invoking the delegate
2. message.Invoke();

Note: <parameters> We can pass parameters as we mentioned to the respective methods.

Example 1: This is the very simple example to understand the basic concepts of the delegate.

Step-1: Define a delegate

Note: we can define the delegate inside the namespace or class.

1. // Step-1: Define a Delegate
2. public delegate void MessageDelegate();
3. public delegate string EmailDelegate(string strEmail);

Create class having names like "Email" and two methods as follow.

1. public class Email
2. {
3. public static string GetEmail(string strEmail)
4. {
5. return "Your Email Id is "+strEmail;
6. }
7. public static void DisplayMessage()
8. {
9. Console.WriteLine("Welcome to CSharp Corner");
10. }
11. }
12. 
    

Step-2: Instantiating the delegate 

1. // Step-2: Instantiating the Delegate.
2. EmailDelegate email = new EmailDelegate(Email.GetEmail);
3. MessageDelegate message = new MessageDelegate(Email.DisplayMessage);

The second way to the binding method to the delegate instance.

1. //OR
2. // Step-2: Binding method to the Delegate instance.
3. EmailDelegate email = Email.GetEmail;
4. MessageDelegate message = Email.DisplayMessage;

Step-3: Invoking the delegate or binding method to delegate instance.

1. // Step-3: Invoking the delegate
2. string strEmail= email.Invoke("shrimantvt@gmail.com");
3. Console.WriteLine(strEmail);
4. message.Invoke();

We can invoke method by using "Invoke()" method or we can pass direct parameter to the delegate instance as following.

1. // Step-3: Invoking the delegate second way
2. email("shrimantvt@gmail.com");
3. message();

Program Code: 

1. using System;
3. namespace DelegateDemo
4. {
5. // Step-1: Define a Delegate
6. public delegate void MessageDelegate();
7. public delegate string EmailDelegate(string strEmail);
8. public class Email
9. {
10. public static string GetEmail(string strEmail)
11. {
12. return "Your Email Id is "+strEmail;
13. }
14. public static void DisplayMessage()
15. {
16. Console.WriteLine("Welcome to CSharp Corner");
17. }
18. }
19. class Program
20. {
21. static void Main(string[] args)
22. {
23. // Step-2: Instantiating the Delegate.
24. EmailDelegate email = new EmailDelegate(Email.GetEmail);
25. MessageDelegate message = new MessageDelegate(Email.DisplayMessage);
27. // Step-3: Invoking the delegate
28. string strEmail= email.Invoke("shrimantvt@gmail.com");
29. Console.WriteLine(strEmail);
30. message.Invoke();
31. Console.ReadLine();
32. }
33. }
34. }

Output:

Type of delegate in c#

• Singlecast Delegate
• Multicast Delegate

• Singlecast Delegates:

Whenever the delegate instance refers to address of the single method. then it is said to be single cast delegate.

Example 2: This is a simple example to understand the basic concept of 'single cast delegate'.

Program Code:

1. using System;
2. namespace DelegateDemo
3. {
4. // Step-1: Define a delegate
5. public delegate double AreaDelegate(double width,double height);
6. public class Rectangle
7. {
8. public static double CalculateArea(double width, double height)
9. {
10. return (width*height);
11. }
12. }
13. class DelegateExampleTwo
14. {
15. static void Main(string[] args)
16. {
17. //Step-2: Instantiating the delegate
18. AreaDelegate area = new AreaDelegate(Rectangle.CalculateArea);
19. // OR
20. //Step-3: Binding method to delegate instance
21. AreaDelegate area1 = Rectangle.CalculateArea;
23. // Step-3: Invoking the Delegate by using invoke method
24. Console.WriteLine("Using invoke method");
25. Console.WriteLine("Area of Rectangle is {0}", area.Invoke(10.10, 20.10));
26. // OR
27. Console.WriteLine("-------------------------------------------------");
28. // Step-3: Invoking the Delegate without using the invoke method
29. Console.WriteLine("Without using invoke method");
30. Console.WriteLine("Area of Rectangle is {0} " , area1(10.10, 20.10));
31. Console.ReadLine();
32. }
33. }
34. }

Note: In the above example the delegate instance is points to only one method like 'CalculateArea'.so that type of delegate is said to be singlecast delegate.

Output:

• Multicast Delegate:

Whenever the delegate instance is points/refers to address of more than one method. then these type of delegate is said to be the multicast delegate.

There are two way calling the multiple methods

• "+="
• "+"

Step-1: Define a delegate.

Note: we can define the delegate inside the namespace or class.

1. // Step-1: Define a delegate
2. public delegate double RectangleDelegate(double width,double height);

Create class name like "Rectangle" having two methods like CalculateArea and CalculatePerimeter of the rectangle as follow.

1. public class Rectangle
2. {
3. public static double CalculateArea(double width, double height)
4. {
5. return (width*height);
6. }
7. public static double CalculatePerimeter(double width, double height)
8. {
9. return 2 * (width + height);
10. }
11. }

Step-2: Instantiating the delegate.

1. //Step-2: Instantiating the delegate
2. RectangleDelegate rectangle = Rectangle.CalculateArea;
3. rectangle += Rectangle.CalculatePerimeter;

Note: You can see the above example, there are one delegate instance points to the more than one methods.

Step-3: Invoking the delegate.

1. // Step-3: Invoking the Delegate by using invoke method
2. Console.WriteLine("Area of Rectangle is {0}", rectangle.Invoke(10.10, 20.10));
3. Console.WriteLine("Perimeter of Rectangle is {0}", rectangle.Invoke(11.10, 21.22));

Program Code:

1. using System;
2. namespace DelegateDemo
3. {
4. // Step-1: Define a delegate
5. public delegate double RectangleDelegate(double width,double height);
6. public class Rectangle
7. {
8. public static double CalculateArea(double width, double height)
9. {
10. return (width*height);
11. }
12. public static double CalculatePerimeter(double width, double height)
13. {
14. return 2 * (width + height);
15. }
16. }
17. class DelegateExampleTwo
18. {
19. static void Main(string[] args)
20. {
21. //Step-2: Instantiating the delegate
22. RectangleDelegate rectangle = Rectangle.CalculateArea;
23. rectangle += Rectangle.CalculatePerimeter;
24. //Step-3: Invoking the Delegate by using invoke method
25. Console.WriteLine("Area of Rectangle is {0}", rectangle.Invoke(10.10, 20.10));
26. Console.WriteLine("Perimeter of Rectangle is {0}", rectangle.Invoke(11.10, 21.22));
27. Console.ReadLine();
28. }
29. }
30. }

Output:

Anonymous Method: You can simply say, It is method without having name. we can use anonymous method in delegates.it is used to write less code. It has high performance as compare to normal delegate.

Advantages:

• Write less code
• High performance

Example 1: This is the simple example to understand the concepts of the anonymous method.

we can take the above same example with having only one method 'CalculateArea'

Step-1: Define a delegate

1. // Step-1: Define a delegate
2. public delegate double RectangleDelegate(double width, double height);

Step-2: Instantiating the delegate

Note: we can see on below example there is no any method declaration. we have directly define method body to the delegate.

1. //Step-2: Instantiating the delegate by using the anonymous method
2. RectangleDelegate rectangle = delegate(double width, double height)
3. {
4. return (width * height);
5. };

Step-3: Invoking the delegate

1. // Step-3: Invoking the Delegate
2. onsole.WriteLine("Area of Rectangle is {0}", rectangle.Invoke(10.10, 20.10));

Program code:

1. using System;
2. namespace DelegateDemo
3. {
4. // Step-1: Define a delegate
5. public delegate double RectangleDelegate(double width, double height);
6. class AnonymousMethod
7. {
8. static void Main(string[] args)
9. {
10. // Step-2: Instantiating the delegate by using anonymous method
11. RectangleDelegate rectangle = delegate(double width, double height)
12. {
13. return (width * height);
14. };
15. // Step-3: Invoking the Delegate
16. Console.WriteLine("Area of Rectangle is {0}", rectangle.Invoke(10.10, 20.10));
17. Console.ReadLine();
18. }
19. }
20. }

Usages of Delegate

• It is used in Event
• It is used in Threading
• It is used to Callback Function
• It is used in Multicasting

I hope you understood the basic concept of the delegate, type of delegate and anonymous method.

If you like then add your valuable feedback that will encourage me to write more articles.

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