Throw exception in try block

Question

    try { 
        if (isFileDownloaded)
            //do stuff
        else
            throw new CustomException()
   } 
   catch (Exception e)
   {
       // something went wrong save error to log
   }
   finally
   {
       //release resources
   }

My question is would the catch catches the ApplicationException thrown in the try block? is it in poor coding style? Should it be written in another way?

Answer 1

Yes, it will catch ApplicationException as it derives from Exception.

Handling the base exception should be fine in most cases unless you need to log or do something with a different type of exception...

try{
    if (isFileDownloaded)
       //do stuff
    else
       throw new ApplicationException();
}
catch(ApplicationException ae)
{
   // log it application exception here...
}

catch(Exception ex)
{
   // log all other exceptions here...
}
finally
{
   // release resources...
}

Answer 2

The catch will catch your exception (and any other that occurs). That being said, I try to avoid writing code like this when possible.

Personally, I see little reason to ever have exception handling (catch) for an exception thrown in the same scope. If you can handle your error in your method - put the exception handling (ie: logging) directly in the try block as well.

Using a catch is more useful, IMO, for catching exceptions thrown by methods within your try block. This would be more useful, for example, if your // do stuff section happened to call a method that raised an exception.

Also, I recommend not catching every exception (Exception e), but rather the specific types of exceptions you can handle correctly. The one exception to this would be if you're rethrowing the exception within your catch - ie: using it for logging purposes but still letting it bubble up the call stack.

Answer 3

Yes the catch would catch your ApplicationException and yes is is poor coding style. As a good general rule only catch specific exception and those that you are going to do something with, like fixing up application state.

Answer 4

Also, FYI, ApplicationException has been deprecated since .NET 2.0 as an exception to derive from. It was never intended as an exception to throw on its own, so you probably shouldn't use it at all.

Answer 5

try { 
    // statements that might throw an error

    if (obj == null)
        throw new Exception("ERROR: Null object"); // allow exception handler to handle error

    // other statements that might throw error
catch (Exception e)
   {
       // exception handler: write to error log
   }
finally
   {
       //release resources
   }

Why I can't I treat the error condition as an exception and re-use the exception handler code to handle it? If I didn't do that, wouldn't I just have to copy and paste the code for exception handling into the if block?