ExceptionHandlingBasics.cs

using System;
using System.IO;

//This program will read from a .txt file

/* Exception Handling Basics
 * 
 * An exception is actually a class that derives from the System.Exception class.
 * The System.Exception class provides valuable information about the exception.
 * example: Message: Gets a message that describes the current exception
 * example: Stack Tracek: Provides the call stack to the line number in the method where the exception occured.
 * 
 * !!Interview Questions!!
 * 
 * Q. Why handle exceptions? 
 * A1. To give the end user useful information regarding the unhandled exception
 * A2. To log important unhandled exception details
 * 
 * Q. Can you tell me a practical application of inheritence?
 * (Using the exception class object to explain inheritence is practical)
 * A. If you want to handle exceptions properly. You will have the most specific exceptions at the top most catch blocks, and the general ones at the bottom most catch blocks.
 *    So that if there is any other exception types, we will know for sure the following catch blocks will handle the exception
 * 
 * ^^ In other words, specific exceptions will be caught before the base general exception, so specific exception blocks should always be on top of the base exception block.
 * 
 */


public class Program
{
    public static void Main()
    {
        StreamReader streamReader = null;

        try //the code that can possibly cause an exception will be in the try block
        {
            streamReader = new StreamReader(@"C:\SampleFiles\Data.txt");
            Console.WriteLine(streamReader.ReadToEnd());
        }
        catch (FileNotFoundException exception) //inherits from System.Exception class (the base class for all exceptions), the catch handles the exception
        {
            Console.WriteLine("The file {0} does not exist", exception.FileName);
        }
        catch (Exception exception) //a parent class reference variable can point to a derived class object
        {
            Console.WriteLine(exception.Message);
        }
        finally //it is good practice to always release resource sin the finally block because the finally block is guaranteed to execute. Exception or not.
        {
            if (streamReader != null)
            {
                streamReader.Close(); //this is important, it will release the streamReader content from memory whether it catches exceptions or not.
                                      //if we were to have the streamReader.Close(); in the try block, and there was an exception, the streamReader would not release
            }
            Console.WriteLine("Finally block reached, streamReader closed.");
        }
        Console.ReadKey();
    }
}