Throwing a particular exception type enables the type itself to identify the problem. It is not necessary, in other words, to catch the exception and use a switch statement on the exception message to determine what action to take in light of the exception. Instead, C# allows for multiple catch blocks, each targeting a specific exception type, as Listing 10.2 shows.
Listing 10.2. Catching Different Exception Types
Listing 10.2 has five catch blocks, each handling a different type of exception. When an exception occurs, the execution will jump to the catch block with the exception type that most closely matches. The closeness of a match is determined by the inheritance chain. For example, even though the exception thrown is of type System.Exception, this "is a" relationship occurs through inheritance because System.ApplicationException derives from System.Exception. Since ApplicationException most closely matches the exception thrown, catch(ApplicationException ...) will catch the exception instead of the catch(Exception ...) block.
Catch blocks must appear in order, from most specific to most general, to avoid a compile error. For example, moving the catch(Exception ...) block before any of the other exceptions will result in a compile error, since all prior exceptions derive from System.Exception at some point in their inheritance chain.