This tutorial will show you how to create your own exceptions by using a class derived from System.ApplicationException.

This is the continuation of the tutorial named Handling and throwing exceptions. I recommend you read that tutorial first.

In that tutorial, at the end you saw how to throw your own exceptions. Here will do the same thing, but a bit more complicated because now you’ll be able to customize the exception.

Create a new Console Application project named customExceptions in Microsoft Visual Studio .NET.

First we’ll have to create the class derived from System.ApplicationException:

// Creating the class derived from System.ApplicationException

public class NumberZeroException : System.ApplicationException

{

   // The constructor that takes msg as a parameter

   public NumberZeroException(string msg) : base(msg)

   {

   }

}

As you can see, it’s nothing more than a class derived from System.ApplicationException with a constructor that takes the msg as a parameter.

Here’s Class1 where we actually throw the exception if the user enters ‘0’.

class Class1

{

   [STAThread]

   static void Main(string[] args)

   {

      // Prompt the user to enter an integer

      Console.WriteLine("Please input an integer: ");

      // Try this block of code

      try

      {

         // Store the input in x

         int x = Convert.ToInt32(Console.ReadLine());

         // If the number entered is 0...

         if(x == 0)

         {

            // ...throw our custom exception with the following message parameter

            throw new NumberZeroException("You are not allowed to enter number 0");

         }

         // Show what the user entered (if it ain't 0)

         Console.WriteLine("You entered: " + x.ToString());

      }

      // Catch the custom exception

      catch(NumberZeroException e)

      {

         // And display the error message

         Console.WriteLine("Error: " + e.Message);

      }

   }

}

The code is fully commented so I suppose you have no problem understanding it.

Now let’s compile it and enter ‘0’ when prompted:

That’s all.