Exception Handling By Sriram . B

Module 7: Exception Handling By SRIRAM . B

Overview 

Exceptions

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Exception Handling Keywords

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Exception Types (System Defined, User Defined)

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Using try and catch

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Using try and finally

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Handling try-catch-finally block

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Throwing Exceptions

Exceptions 

An exception is an erroneous situation that occurs during program execution.

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 Exception-handling provides a structured and uniform way of handling system-

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All exceptions are represented by an instance of a predefined class,

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level and application-level errors.

System.Exception.

Some of the system level exceptions are :

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A division by zero A reference to a Null value

Exception Handling Keywords 

Try

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Catch

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finally

System Defined Exceptions 

Exception (Base Class)

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IndexOutOfRangeException

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NullReferenceException

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ArgumentException

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ArrayTypeMismatchException

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OverflowException

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ArithmeticException

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DivideByZeroException

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InvalidOperationException

User Defined Exceptions 

Besides the default or system exceptions, a programmer can also creates his own set of exceptions. The advantage is :-

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It can hold more information about the error condition than a standard class.

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The user can tailor the catch blocks to the specific exception type, instead of catching a generic exception.

Try Block A try block guards the statements that may throw an exception. try { //statements that may cause an exception

}

Using try and catch Block You can associate an exception-handler with the try block by providing one or more catch-handlers immediately after the try block. try { //statements that may cause an exception } catch (…) { //error handling code }

Using try and finally block The finally block is used to execute a given set of statements, irrespective of whether an exception is thrown or not. try { //statements that may cause an exception } finally { //statements to be executed }

Handling try-catch-finally block 

Since catch performs exception handling and finally performs the cleanup, the best approach is to merge both applications.

Syntax :try { //statements that may cause an exception } catch (…) { //error handling code } finally { //statements to be executed } 

Finally block 

If no exception is thrown from the try block, control passes to the finally block after the closing brace of the try block.

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If no catch block is specified or none of the catch blocks match the exception.

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If a matching catch block exists, it gets executed, after which the catch block control comes to finally block.

Throwing Exceptions 

To throw an exception explicitly one has to use the throw statement.

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Helpful for throwing user defined exceptions

Example 1 – Exception Handling using System; namespace Exception Handling { class Add_nums { public static void add(int a, int b) { int res=a/b; Console.WriteLine(res); } public static void Main() { Add_nums.add(10,0); } } Result in Exception

Example 2 – Exception Handling Using System; namespace Exception Handling { public class excep1 { static void Main(string[] arg) { int[] a ={ 2, 4, 12, 56, 23 }; for (int i = 0; i <= 5; i++) try { Console.WriteLine("The {0}th element of the array is {1}", i, a[i]); } catch (IndexOutOfRangeException e)

Example 2 – Exception Handling.. { Console.WriteLine("An Exception has occured"); Console.WriteLine("The description is } } } }

" + e);

Exception Handling Flashback 

Exceptions

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Exception Handling Keywords

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Exception Types (System Defined, User Defined)

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Using try and catch

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Using try and finally

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Handling try-catch-finally block

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Throwing Exceptions

Session Ends

Exercise

Relax