Csharp/CSharp Tutorial/Language Basics/Finally

Dispose a StreamWriter in finally block

using System;
using System.IO;
public sealed class MainClass
{
    static void Main(){
        StreamWriter sw = new StreamWriter("Output.txt");
        try {
            sw.WriteLine( "This is a test of the emergency dispose mechanism" );
        }
        finally {
            if( sw != null ) {
                ((IDisposable)sw).Dispose();
            }
        }
    }
}

finally block is always executed even if an exception was thrown in the try

using System;
using System.IO;
class Processor
{
    public void ProcessFile()
    {
        FileStream f = new FileStream("wrongNameFile.txt", FileMode.Open);
        try
        {
            StreamReader t = new StreamReader(f);
            string    line;
            while ((line = t.ReadLine()) != null)
            {
                Console.WriteLine(line);
            }
        }
        finally
        {
            f.Close();
        }
    }
}
class Test
{
    public static void Main()
    {
        Processor processor = new Processor();
        try
        {
            processor.ProcessFile();
        }
        catch (Exception e)
        {
            Console.WriteLine("Exception: {0}", e);
        }
    }
}

Exception: System.IO.FileNotFoundException: Could not find file "C:\Java_Dev\WEB\dev\CSharp\wrongNam
eFile.txt".
File name: "C:\Java_Dev\WEB\dev\CSharp\wrongNameFile.txt"
   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean
 useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, St
ring msgPath, Boolean bFromProxy)
   at System.IO.FileStream..ctor(String path, FileMode mode)
   at Processor.ProcessFile()
   at Test.Main()

Using finally

Sometimes you can define a block of code that will execute when a try/catch block is left.

The general form of a try/catch that includes finally is shown here:

try {
        // block of code to monitor for errors
    }
    catch (ExcepType1 exOb) {
        // handler for ExcepType1 
    }
    catch (ExcepType2 exOb) {
        // handler for ExcepType2 
    }
    .
    .
    .
    finally {
        // finally code
    }