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The case against checked exceptions

Asked 2009-03-05T08:18:54.603
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For a number of years now I have been unable to get a decent answer to the following question: why are some developers so against checked exceptions? I have had numerous conversations, read things on blogs, read what Bruce Eckel had to say (the first person I saw speak out against them).

I am currently writing some new code and paying very careful attention to how I deal with exceptions. I am trying to see the point of view of the "we don't like checked exceptions" crowd and I still cannot see it.

Every conversation I have ends with the same question going unanswered... let me set it up:

In general (from how Java was designed),

  • Error is for things that should never be caught (VM has a peanut allergy and someone dropped a jar of peanuts on it)
  • RuntimeException is for things that the programmer did wrong (programmer walked off the end of an array)
  • Exception (except RuntimeException) is for things that are out of the programmer's control (disk fills up while writing to the file system, file handle limit for the process has been reached and you cannot open any more files)
  • Throwable is simply the parent of all of the exception types.

A common argument I hear is that if an exception happens then all the developer is going to do is exit the program.

Another common argument I hear is that checked exceptions make it harder to refactor code.

For the "all I am going to do is exit" argument I say that even if you are exiting you need to display a reasonable error message. If you are just punting on handling errors then your users won't be overly happy when the program exits without a clear indication of why.

For the "it makes it hard to refactor" crowd, that indicates that the proper level of abstraction wasn't chosen. Rather than declare a method throws an IOException,

java exception checked-exceptions
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Here's one argument against checked exceptions (from joelonsoftware.com):

The reasoning is that I consider exceptions to be no better than "goto's", considered harmful since the 1960s, in that they create an abrupt jump from one point of code to another. In fact they are significantly worse than goto's:

  • They are invisible in the source code. Looking at a block of code, including functions which may or may not throw exceptions, there is no way to see which exceptions might be thrown and from where. This means that even careful code inspection doesn't reveal potential bugs.
  • They create too many possible exit points for a function. To write correct code, you really have to think about every possible code path through your function. Every time you call a function that can raise an exception and don't catch it on the spot, you create opportunities for surprise bugs caused by functions that terminated abruptly, leaving data in an inconsistent state, or other code paths that you didn't think about.
answered 2009-03-05T09:12:51.040

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