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Message:

Exceptions are free unless thrown

Posted by Bill Venners on 10 Jul 1998, 8:55 AM

> For me, this whole thing stemmed from reconstituting Objects after serialization. Some data members were declared transient (or didn't implement Serializable). So I was faced with the decision of cluttering up constructors with "initialization" methods, recreating the data members on readObject (directly or using the same "initialization" methods), wrapping their usage in a try/catch clause (looking for NullPointerExceptions) or just checking to see if the memebers != null. I opted for the try/catch (for better or worse) since the members really have one time that they were actually == null. So I guess the question is, "If I know that 99.999% of the time I will not throw an Exception, what is the cost of a try/catch clause?"

I think I understand your situation. The answer to your question,
I believe, is that if you don't actually throw an exception,
then having a try/catch clause is "free" from the perpective
of execution time. The JVM has to check every usage of the
reference for null, because whether or not you have a catch
clause for NullPointerException, the VM is going to throw it
if you try to use a null reference. (Or, if the VM is able to
optimize out the check for null, it will not check for null
regardless of whether you have a catch clause or not.)

So the VM has to do the same thing as it executes along whether
or not you have the try/catch there. It is only if the exception
is actually thrown that the performance hit comes. To get an
idea how expensive a throw/catch is, check out:

http://www.javaworld.com/javaworld/jw-04-1997/optimize/Benchmark_Results.html

The only other cost I can think of that would come from having
try/catch blocks is that it could make your class file
bigger, which could slow download times, but this is likely
going to be minutia.

bv