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Message:

checked vs. unchecked

Posted by Jonathan Brumley on 06 Jul 1998, 3:06 PM

Bill, I like your advice that checked exceptions should be thrown when you expect the client will know how to and should deal with them, and unchecked exceptions should be thrown indicating incorrect usage.

One issue I deal with a lot is implementing classes in a distributed environment. When I define an interface for these classes, I have debated whether it is better to define NetworkException faults as checked or unchecked exceptions. This is certainly the case where you expect that the client should deal with these types of faults. But, then you have to ask, will the immediate client know HOW to deal with them? Or will someone higher up his stack know how to? The simple answer to this question is that the immediate client should simply rethrow the exception if this is the case. But, this approach tends to clutter up a lot of code that you may not want to be network aware. Often the immediate client of the remote object is not aware that the object is really remote. i.e. consider a File I/O system where the underlying implementation is an NFS. In applications, network fault handlers are typically implemented very high up in the application stack, because they often require user interaction to fix.

Also, the rarity of your exception depends on your network. If you're on an Ethernet LAN, messages between nodes are extremely reliable, and somewhat fast - so a remote method invocation is almost as reliable as invoking a local method. (Someone could pop out your memory chips almost as easily as unplugging you from the LAN). However, if you're communicating between clients over a modem, network faults occur very frequently, and clients typically have to know the difference since modems are so slow.

RMI forces you to define a RemoteException for every method, whereas some other ORBs like Voyager allow you to define your preferred exception model.

So, my question is: checked or unchecked?

• Checked or unchecked with remote objects Mike Mannion 08 Jul 1998, 1:07 AM (0)