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Exceptional Circumstance Exception Classes in C#
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: 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.
Syntax
·
Assuming a block raises an exception, a method catches an
exception using a combination of the try and catch keywords. A try/catch block
is placed around the code that might generate an exception. Code within a
try/catch block is referred to as protected code, and the syntax for using
try/catch looks like the following:
try
{
// statements causing exception
}
catch(ExceptionName
e1 )
{
// error handling code
}
catch(ExceptionName
e2 )
{
// error handling code
}
catch(ExceptionNameeN
)
{
// error handling code
}
finally
{
// statements to be executed
}
You can
list down multiple catch statements to catch different type of exceptions in
case your try block raises more than one exception in different situations.
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 theSystem.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.
|
Handling Exceptions
Example 1
usingSystem;
namespaceErrorHandlingApplication
{
classDivNumbers
{
int result;
DivNumbers()
{
result=0;
}
publicvoid division(int num1,int num2)
{
try
{
result= num1 / num2;
}
catch(DivideByZeroException e)
{
Console.WriteLine("Exception caught: {0}", e);
}
finally
{
.WriteLine("Result: {0}", result);
}
}
staticvoidMain(string[]args)
{
DivNumbers d =newDivNumbers();
d.division(25,0);
Console.ReadKey();
}
}
}
Handling Exceptions
Example 2
namespaceExcHan
{
classDivNumbers
{
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();
}
}
}
Handling Exceptions
Example 3
namespaceExcHan
{
class
Program
{
static
void Main(string[] args)
{
int[]
numbers = new int[2];
try
{
numbers[0]
= 23;
numbers[1]
= 32;
numbers[2]
= 32;
foreach
(inti in numbers)
Console.WriteLine(i);
}
catch
(IndexOutOfRangeException ex)
{
Console.WriteLine("An
index was out of range!"+ex.Message);
}
catch
(Exception ex)
{
Console.WriteLine("Some
sort of error occured: " + ex.Message);
}
finally
{
Console.WriteLine("It's
the end of our try block. Time to clean up!");
}
Console.ReadLine();
Console.ReadKey();
}
}
}
Creating User-Defined
Exceptions
You can also define your own exception.
User-defined exception classes are derived from the ApplicationException class. The following example
demonstrates this:
usingSystem;
namespaceUserDefinedException
{
classTestTemperature
{
staticvoidMain(string[]args)
{
Temperature temp =newTemperature();
try
{
temp.showTemp();
}
catch(TempIsZeroException e)
{
Console.WriteLine("TempIsZeroException: {0}",e.Message);
}
Console.ReadKey();
}
}
}
publicclassTempIsZeroException:ApplicationException
{
publicTempIsZeroException(string message):base(message)
{
}
}
publicclassTemperature
{
int temperature =0;
publicvoidshowTemp()
{
if(temperature ==0)
{
throw(newTempIsZeroException("Zero Temperature found"));
}
else
{
Console.WriteLine("Temperature: {0}", temperature);
}
}
}
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