Path: csiph.com!optima2.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!us.feeder.erje.net!newsfeed.fsmpi.rwth-aachen.de!newsfeed.straub-nv.de!eternal-september.org!feeder.eternal-september.org!mx02.eternal-september.org!.POSTED!not-for-mail From: Eric Sosman Newsgroups: comp.lang.java.programmer Subject: Re: [JLS] new long[0][ -1 ] Date: Fri, 10 Jul 2015 09:45:25 -0400 Organization: A noiseless patient Spider Lines: 49 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Fri, 10 Jul 2015 13:44:04 +0000 (UTC) Injection-Info: mx02.eternal-september.org; posting-host="858a9d65d95f4ea4d355bd116aa2cdbf"; logging-data="9014"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+S8tKdQc3bjOjc3c5HkfnG" User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.0.1 In-Reply-To: Cancel-Lock: sha1:GUup6MQNUPt+DLAXWiDW5mty4sY= Xref: csiph.com comp.lang.java.programmer:31980 On 7/10/2015 8:58 AM, Andreas Leitgeb wrote: > Eric Sosman wrote: >> On 7/10/2015 7:52 AM, Andreas Leitgeb wrote: >>> I've had a look at the JLS to find out about the more or less special >>> case of a 2-dimensional array, whose first(outer) dimension is 0, but >>> I didn't find any extra mention of that case. >>> >>> From what I read, it would evaluate *all* the dimensions, then check >>> if any of them is negative. >>> >>> But if first dimension is 0, then the loop shown in the "equivalent as"- >>> code sample would not get its body run even once, so actually it wouldn't >>> even notice if any of the further dimensions was negative. >>> >>> What would be an accurate *purely JLS-based* prediction for >>> new long[0][-1] >>> (not caring about actual existing JVM implementations) ? >> >> Intriguing question, but easily answered. 15.10.2, second >> bullet, second sub-bullet: >> >> "Next, the values of the dimension expressions are checked. >> If the value of any DimExpr expression is less than zero, >> then a NegativeArraySizeException is thrown." > > My mistake was to generalize the first example in 15.10.1-2 . > > On second thought, the equivalence in the example-block is correct. > It just cannot be generalized from dimensions 3,3 to "any" (like 0,-1), > as for dims 0,-1 the compact form has to throw a NASE, while the > alternative code doesn't. > > Thanks. Knot in my brain dissolved. :-) You're welcome. But contemplating the uses of an array with fewer than zero elements has tied what remains of my brain in a knot that may not dissolve until my brain itself does ... :-) What use might we make of a minus-sized array? Perhaps it could model the old joke about a biologist, an engineer, and a mathematician at a sidewalk cafe. They see two people enter a building across the street, and a little later three people emerge. "They have reproduced," says the biologist. "Observational error," says the engineer. And the mathematician observes "If somebody now goes inside, the building will be empty." -- esosman@comcast-dot-net.invalid "Don't be afraid of work. Make work afraid of you." -- TLM