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Java Forum / General / April 2008my thread of basic Java questions
Why is the following true?: (ok || (n1 < 0)) And what the heck is "ok"? My guess: any String or character or whatever is "true" on its own, since it exists. Thus, "ok" could be replaced by "dinosaur", and the answer to the question would still be true. > Why is the following true?: > [quoted text clipped - 5 lines] > since it exists. Thus, "ok" could be replaced by "dinosaur", and the > answer to the question would still be true. It isn't true, and strings in Java have double quotes around them. ok is obviously a variable that's been declared elsewhere, just like n1. > denim_ge...@hotmail.com wrote: > > Why is the following true?: [quoted text clipped - 10 lines] > > ok is obviously a variable that's been declared elsewhere, just like n1. It's true... I'm looking at the answer key right now... int dinosaur = 0; dinosaur == true ? >> denim_ge...@hotmail.com wrote: >>> Why is the following true?: [quoted text clipped - 12 lines] > > dinosaur == true ? It's false. I don't care about your answer key. Get a compiler and try it, or better yet learn the language. Your latest one here is wrong too, ints aren't even comparable to booleans.: init: deps-jar: Compiling 1 source file to C:\Users\Brenden\Dev\misc\FinalizeTest\build\classes C:\Users\Brenden\Dev\misc\FinalizeTest\src\finalizetest\Main.java:31: incomparable types: int and boolean if( dinosaur == true ) 1 error BUILD FAILED (total time: 2 seconds) > denim_ge...@hotmail.com wrote: > >> denim_ge...@hotmail.com wrote: [quoted text clipped - 28 lines] > 1 error > BUILD FAILED (total time: 2 seconds) I know the language, hence why I was confused as to this "reliable" answer key. >>> denim_ge...@hotmail.com wrote: >>>> Why is the following true?: [quoted text clipped - 18 lines] > Your latest one here is wrong too, ints aren't even comparable to > booleans.: [ SNIP ] This question brings up the always popular programming trivia contest...what are the truth values in various programming languages? Not always easy to remember... For example, in awk "0" is true because it's a non-null string value. However, in Perl "0" is false (but "0.0" is true). Apparently in REBOL the integer 0 is true. Does the language in question (1) use two boolean values, or (2) does it define truth values for all values of datatypes, or (3) does it define two boolean values *and* also truth values for values of other datatypes? Example of #3 being Javascript. Then there's the convention in UNIX that a program is considered to have succeeded if it sets an exit code of 0, which can catch the novice shell script programmer by surprise... I think there was an attempt to design a bool class in C++ quite some back but they couldn't quite design one that was completely correct, hence the bool datatype. Of course you can still initialize a bool with 0... AHS On Sat, 12 Apr 2008 23:18:07 -0700, Mark Space <markspace@sbc.global.net> wrote, quoted or indirectly quoted someone who said : >I don't care about your answer key. Sounds like that Monty Python English phrase book for Bulgarians.  SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com >dinosaur == true ? That is equivalent to asking if 1 is true. It is a meaningless question in Java.. In C, any int != 0 is considered true. In java an int has no meaning as a boolean. You would have to say something like int dinosaur; ... boolean isBaby = dinosaur < 1; which might or might not be true. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com don't you need a boolean or something that can be converted to a boolean by the compiler for that to work? > Why is the following true?: > [quoted text clipped - 5 lines] > since it exists. Thus, "ok" could be replaced by "dinosaur", and the > answer to the question would still be true. What is ok declared as ? Arne >> Why is the following true?: >> [quoted text clipped - 7 lines] > > What is ok declared as ? And what is its value ? Arne > > denim_ge...@hotmail.com wrote: > >> Why is the following true?: [quoted text clipped - 12 lines] > > Arne boolean ok = true; int n1 = 100; int n2 = 0; They forgot to put that in the question. I guess it makes sense now. >>> denim_ge...@hotmail.com wrote: >>>> Why is the following true?: [quoted text clipped - 11 lines] > > They forgot to put that in the question. I guess it makes sense now. Yes. (ok || (n1 < 0)) = (true || (100 > 0)) = (true || false) = true Arne denim_genes@hotmail.com wrote: >> Why is the following true?: >> (ok || (n1 < 0)) >> boolean ok = true; >> int n1 = 100; >> int n2 = 0; >> >> They forgot to put that in the question. I guess it makes sense now. > Yes. > > (ok || (n1 < 0)) = (true || (100 < 0)) = (true || false) = true Nitpick: Since || is an early-out operator, the (100 < 0) clause is never evaluated once 'ok' is found to be true. (ok || (n1 < 0)) == (true || <unevaluated>) == true SignatureLew > denim_genes@hotmail.com wrote: >>> Why is the following true?: [quoted text clipped - 14 lines] > > (ok || (n1 < 0)) == (true || <unevaluated>) == true Good point. If it is one of those Java language test, then that could be considered important. Arne >> denim_genes@hotmail.com wrote: >>>> Why is the following true?: [quoted text clipped - 19 lines] > If it is one of those Java language test, then that could be > considered important. Yup, if( ok || (n1++ < 0) ){}, what is the value of n1 after this statement? Still 100 because the ++ never got evaluated. I'd like to see a link to this "answer key" the OP is referring too. If it's really Java and not some other language, I don't think it's a very good one. But I'd like to check it out myself. >>> denim_genes@hotmail.com wrote: >>>>> Why is the following true?: [quoted text clipped - 28 lines] > it's really Java and not some other language, I don't think it's a very > good one. But I'd like to check it out myself. That type of code is not good code, but is exactly what some tests like to check. Arne > That type of code is not good code, but is exactly what some tests > like to check. Yup, exactly what I was thinking. Not a good pattern, but something that you would expect to see on a test. > > That type of code is not good code, but is exactly what some tests > > like to check. > > Yup, exactly what I was thinking. Not a good pattern, but something > that you would expect to see on a test. This is an introductory programming course, hence the poor quality of questions (if that's any excuse). I found myself handing in assignments with increased efficiency (not having variables I didn't need) and error-checking when they weren't even on the grading criteria. Really a basic course. Which is why I'm pissed... I totally didn't study anything related to making classes (no time), so I may have lost marks on that part of the exam I just wrote. I assumed I would handle their basic questions, but they did ask some rather weird ones. Anyway, thnx. Lew wrote: >> Nitpick: Since || is an early-out operator, the (100 < 0) clause is >> never evaluated once 'ok' is found to be true. >> >> (ok || (n1 < 0)) == (true || <unevaluated>) == true > Good point. > > If it is one of those Java language test, then that could be > considered important. It could also signify if the expressions under evaluation have side effects. if ( isSecurityFine() || destroyAllFiles() ) vs. if ( isSecurityFine() | destroyAllFiles() ) Either one will ensure that spies cannot read the contents. Only one will give you the opportunity to do so absent a breach. SignatureLew > Nitpick: Since || is an early-out operator, the (100 < 0) clause is > never evaluated once 'ok' is found to be true. > > (ok || (n1 < 0)) == (true || <unevaluated>) == true Partly related I often use: if (object != null && object.hasSomeCondition) { executeFooBaa(); } I rely on the fact that the second part of the condition never gets executed if object == null. This seems a little sloppy on my behalf but it looks nicer than: if (object != null) { if (object.hasSomeCondition) { executeFooBaa(); } } What does everyone else do? Lionel. >> Nitpick: Since || is an early-out operator, the (100 < 0) clause is >> never evaluated once 'ok' is found to be true. [quoted text clipped - 9 lines] > I rely on the fact that the second part of the condition never gets > executed if object == null. This seems a little sloppy on my behalf How in the world do you rate something with such economy of expression yet with no sacrifice in clarity "sloppy"? Especially when it's such a universal idiom? SignatureLew > if (object != null && object.hasSomeCondition) { > executeFooBaa(); > } When Arne called my code "not good," I think he was referring to the use of side effects and the post increment ++ operator in a comparison. Or at least I assumed he was. Short circuit operators like above are fine. Side effects can be questionable. ++ and -- are both especially subject to abuse. >> if (object != null && object.hasSomeCondition) { >> executeFooBaa(); [quoted text clipped - 6 lines] > Short circuit operators like above are fine. Side effects can be > questionable. ++ and -- are both especially subject to abuse. I use that construct myself. Extremely strictly speaking then crashing versus not crashing could be considered a side effect. But I don't think this is a real problem. The ++ and -- could be a problem, but even those are not the worst. It is: if(something || sometmethodthatchangestate()) that really make it hard to follow the logic. Arne >boolean ok = true; Why the expression ok || n1 <0 is true regardless of the value of n1 is a property of || and |. See http://mindprod.com/jgloss/mccarthyoroperator.html http://mindprod.com/jgloss/oroperator.html SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com >Why is the following true?: > >(ok || (n1 < 0)) it isn't. It is true if and only if the boolean variable ok is true or if n1 < 0. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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