C# finally Block
In this chapter you will learn:
- What is finally Block
- How to use finally block in exception handling
- Example for finally Block
- finally is always executed
- Dispose a StreamWriter in finally block
Description
A finally block always executes-whether or not an exception is thrown and
whether or not the try block runs to completion.
finally blocks are typically used for cleanup code.
Syntax
The general form of a try/catch that includes finally is shown here:
try {/*from ww w .ja v a 2 s.c o m*/
// block of code to monitor for errors
}
catch (ExcepType1 exOb) {
// handler for ExcepType1
}
catch (ExcepType2 exOb) {
// handler for ExcepType2
}
.
.
.
finally {
// finally code
}
Example
The finally block will be executed whenever execution leaves a try/catch block.
using System; /*from w w w . j ava 2s . c o m*/
class MainClass {
public static void Main() {
Console.WriteLine("Receiving ");
try {
int i=1, j=0;
i = i/j;
}
catch (DivideByZeroException) {
Console.WriteLine("Can't divide by Zero!");
return;
}
catch (IndexOutOfRangeException) {
Console.WriteLine("No matching element found.");
}
finally {
Console.WriteLine("Leaving try.");
}
}
}
The code above generates the following result.
Example 2
finally block is always executed
even if an exception was thrown in the try.
using System;/*w w w .j ava 2 s . c om*/
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);
}
}
}
The code above generates the following result.
Example 3
Dispose a StreamWriter in finally block
using System;/*from w w w . j a v a 2s .c o m*/
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();
}
}
}
}
The code above generates the following result.
Next chapter...
What you will learn in the next chapter:
- What is C# throw statement
- Throwing an exception
- Example throw statement
- Rethrowing an exception
- Throw Exception in finally statement