VB.Net - Exception Handling

An exception is a problem that arises during the execution of a program. An 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. VB.Net exception handling is built upon four keywords - Try, Catch, Finally and Throw.

• Try − A Try block identifies a block of code for which particular exceptions will be activated. It's 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 will raise 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
     [ tryStatements ]
     [ Exit Try ]
  [ Catch [ exception [ As type ] ] [ When expression ]
     [ catchStatements ]
     [ Exit Try ] ]
  [ Catch ... ]
  [ Finally
     [ finallyStatements ] ]
  End Try