Q: What is the problem with checked exceptions?
A: With checked exceptions, you have to either catch exceptions thrown by the methods you call, or mention the exception in the throws clause of your method. Because of the tedium of mentioning each exception in the throws clause, some programmers may take the shortcut of swallowing exceptions.

Q: What is meant by swallowing an exception?
A: You should only catch exceptions that you are prepared to handle. Otherwise, if you catch an exception and ignore it (or log it), you are "swallowing" the exception. As a result, code higher up the call chain that may be prepared to handle the exception will never see the exception.

Q: Does C# solve the problem of swallowed exceptions?
A: No. In fact, C# requires it! Methods in C# cannot specify the exceptions it may throw. The documentation of the method you wish to call may mention the list of exceptions you can expect. But this list of exceptions is not enforced by the compiler, and is not guaranteed to be exhaustive. Also, since the list of exceptions is not part of the contract, the method can be revised at any time and a new exception that you didn't know about can be thrown.

Since there is no previously agreed upon list of exceptions, you are left with no option but to catch all exceptions if you want to recover from an exception (such as by offering to connect to an alternate database if the primary database is down, etc.)

Obviously, if you catch all exceptions, you will end up swallowing some of them.

Q: What other problems exist with C# exceptions?
A: Often in C#, if you have multiple implementations of an interface, each of those implementations may have their own disjoint exception hierarchies. (i.e., the exception hierarchies have no common classes other than System.Exception.) Example: ADO.NET. This makes it impossible for generic code (i.e., code that can use any of those implementations) to recover from exceptions generically without catching all exceptions (i.e., System.Exception.)

Again, if you catch all exceptions you will end up swallowing some of them.

Q: What can we conclude from all this?
A: Unchecked exceptions results in shorter but less robust code.

[Back to Index]