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From: Eric Sosman <esosman@ieee-dot-org.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: Using Enumerated Types as Array Indexes
Date: Wed, 17 Aug 2011 21:50:06 -0400
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On 8/17/2011 7:09 PM, markspace wrote:
> On 8/17/2011 10:02 AM, Robert Klemme wrote:
>
>> 1. There was an AtomicInteger initialized at startup with 0 which for
>> every request coming into that system was incremented in a thread safe
>> manner (incrementAndGet()).
>
>
> I'd be shocked if an int actually overflowed when counting requests like
> this, but that's all I can think of. 2^31 is such a huge number, I
> didn't think you could get there in practical cases.

     He *did* write "two months of uninterrupted [...] usage."  Two
months ~= 60 days ~= 5 megaseconds, so a 2G counter overflows if it
increments at ~400 Hz or more, give or take a few backs of envelopes.

> Assuming that the AtomicInteger did overflow, then n % y produces
> negative numbers if n is negative, a clear AIOOB.
>
> Try : arr[ Math.abs( n ) % arr.length ];

     Bzzzzt!  Thank you for playing, go back to the rear of the line.
While awaiting your next opportunity, ponder: What is the sign of
Math.abs(Integer.MIN_VALUE)?

-- 
Eric Sosman
esosman@ieee-dot-org.invalid