Exception Handling

 Exception Handlin

An exception is a problem that arises during the execution of a program. A C# exception is a response to an exceptional circumstance that arises while a program is running, such as an attempt to divide by zero.

Exceptions provide a way to transfer control from one part of a program to another. C# exception handling is built upon four keywords: try, catch, finally, and throw.

·        try: A try block identifies a block of code for which particular exceptions is activated. It is followed by one or more catch blocks.

·        catch: A program catches an exception with an exception handler at the place in a program where you want to handle the problem. The catch keyword indicates the catching of an exception.

·        finally: The finally block is used to execute a given set of statements, whether an exception is thrown or not thrown. For example, if you open a file, it must be closed whether an exception is raised or not.

·        throw: A program throws an exception when a problem shows up. This is done using a throw keyword.

·         try

·         {

·            // statements causing exception

·         }

·         catch( ExceptionName e1 )

·         {

·            // error handling code

·         }

·         catch( ExceptionName e2 )

·         {

·            // error handling code

·         }

·         catch( ExceptionName eN )

·         {

·            // error handling code

·         }

·         finally

·         {

·            // statements to be executed

·         }

Exception Classes in C#

C# exceptions are represented by classes. The exception classes in C# are mainly directly or indirectly derived from the System.Exception class. Some of the exception classes derived from the System.Exception class are the System.ApplicationException and System.SystemException classes.

The System.ApplicationException class supports exceptions generated by application programs. Hence the exceptions defined by the programmers should derive from this class.

The System.SystemException class is the base class for all predefined system exception.

The following table provides some of the predefined exception classes derived from the Sytem.SystemException class:

Exception Class	Description
System.IO.IOException	Handles I/O errors.
System.IndexOutOfRangeException	Handles errors generated when a method refers to an array index out of range.
System.ArrayTypeMismatchException	Handles errors generated when type is mismatched with the array type.
System.NullReferenceException	Handles errors generated from deferencing a null object.
System.DivideByZeroException	Handles errors generated from dividing a dividend with zero.
System.InvalidCastException	Handles errors generated during typecasting.
System.OutOfMemoryException	Handles errors generated from insufficient free memory.
System.StackOverflowException	Handles errors generated from stack overflow.

using System;

namespace ErrorHandlingApplication

{

   class DivNumbers

   {

      int result;

      DivNumbers()

      {

         result = 0;

      }

      public void division(int num1, int num2)

      {

         try

         {

            result = num1 / num2;

         }

         catch (DivideByZeroException e)

         {

            Console.WriteLine("Exception caught: {0}", e);

         }

         finally

         {

            Console.WriteLine("Result: {0}", result);

         }

      }

      static void Main(string[] args)

      {

         DivNumbers d = new DivNumbers();

         d.division(25, 0);

         Console.ReadKey();

      }

   }

}

When the above code is compiled and executed, it produces the following result:

Exception caught: System.DivideByZeroException: Attempted to divide by zero. 

at ...

Result: 0

Throws

public class ThrowTest2

    {

        static int GetNumber(int index)

        {

            int[] nums = { 300, 600, 900 };

            if (index > nums.Length)

            {

                throw new IndexOutOfRangeException();

            }

            return nums[index];

        }

        static void Main() 

        {

            int result = GetNumber(3);

        }

    }

    /*

        Output:

        The System.IndexOutOfRangeException exception occurs.

    */