Quoting from [1]:
If the catch block completes abruptly for reason R, then the finally block is executed. Then there is a choice:
If the finally block completes normally, then the try statement completes abruptly for reason R.
If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and reason R is discarded).
(Emphasis mine)
Conclusion
It is unwise to
NOT catch Exceptions or throw Exceptions in a Finally block. An exception that is thrown in the finally block, may cause an exception in the try to be discarded. This can lead to errors that obscure the original error.
I can imagine how easy this can happen, for example, if there is an Exception in the try in such a fashion that the closing of resources in the Finally clause will also throw an Exception.
In fact, that is what happened at work, and threw me for a loop when attempting to debug.
Addendum
Luckily, with Java 7
2, when using the try-with-resources statement, this problem belongs to the past. Of course this only belongs to the past, if your try-catch-finally can be replaced with a try-with-resources.
To be specific, when using
try-with-resources only the exception in the
try is thrown. Subsequent exceptions, caused by the closing of the resources, are suppressed. But even these exceptions can still be recovered, by requesting all suppressed exceptions from the exception thrown in the try block
3.
(Addendum added: 23 july 2015)
References
- [1] JLS - 14.20.2. Execution of try-finally and try-catch-finally
- http://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.20.2
- [2] The Java™ Tutorials - The try-with-resources Statement
- https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html
- [3] JavaDoc - Throwable.getSupressed()
- http://docs.oracle.com/javase/8/docs/api/java/lang/Throwable.html#getSuppressed--
Well, I managed to get my certification for Professional Scrum Developer on Thursday, the 16th of July 2015. Wasn't terribly hard.