Programs written in VB.NET utilize the Throw-Catch model of exception handling when dealing with errors. The classes found in the.NET Framework use this model for handling errors, but the classes you develop must generate their own exceptions for handling errors. In this chapter, we discuss how exception classes are created and how to use them. We start the chapter with a review of the Throw-Catch model, which includes the Try-Catch-Finally statement.

EXCEPTION HANDLING IN VB.NET

The term VB.NET uses for errors that occur in executing code is exception. Writing code that deals with errors in a program is called exception handling. Exception handling in VB.NET consists of writing code that watches for exceptions when they're thrown and writing code that causes an exception to be thrown when an error condition arises. A VB.NET programmer is not responsible for always writing exception-generating code since the.NET Framework classes throw their own exceptions.

For example, trying to open a file that doesn't exist throws an exception because there was no file to open. This object is called FileNotFoundException. In the next section we examine how to write code to catch built-in exception objects.

Writing Exception-Handling Code

As we've discussed, trying to open a nonexistent file throws an exception. For our program to recognize the exception, we have to use a special construct—the Try-Catch-Finally statement.