floating point

Discussion in 'Java' started by bob smith, Jul 24, 2012.

  1. bob smith

    bob smith Guest

    I can never remember this.

    Let's say you have an integer and a float in an operation. Is the result always a float?

    For instance;

    int x = 5;

    Is x/10.0f definitely a float? Is this true for all ops?
     
    bob smith, Jul 24, 2012
    #1
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  2. bob smith

    markspace Guest

    On 7/24/2012 12:57 PM, bob smith wrote:
    > I can never remember this.
    >
    > Let's say you have an integer and a float in an operation. Is the result always a float?



    You can just try this to see what you get, or read the JLS. From
    memory, I'm 90% sure that ints will be promoted to floats. I'm not sure
    how order of operations affects this. In the expression (1+1)/2.0f,
    does the addition use floats or ints? I'm not sure, but I think ints.
     
    markspace, Jul 24, 2012
    #2
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  3. bob smith

    Lew Guest

    markspace wrote:
    > bob smith wrote:
    >> I can never remember this.
    >>
    >> Let's say you have an integer and a float in an operation. Is the result always a float?

    >
    >
    > You can just try this to see what you get, or read the JLS. From


    Excellent advice.

    "Just trying it" could obscure some of the intermediate promotions.

    > memory, I'm 90% sure that ints will be promoted to floats. I'm not sure
    > how order of operations affects this. In the expression (1+1)/2.0f,
    > does the addition use floats or ints? I'm not sure, but I think ints.


    From the JLS:

    "The left-hand operand of a binary operator appears to be fully evaluated
    before any part of the right-hand operand is evaluated."

    "The Java programming language respects the order of evaluation indicated
    explicitly by parentheses and implicitly by operator precedence."

    So, yes, the parenthesized addition is done as an 'int' addition.

    "5.6. Numeric Promotions

    "Numeric promotion is applied to the operands of an arithmetic operator.
    Numeric promotion contexts allow the use of:

    " an identity conversion (§5.1.1)
    " a widening primitive conversion (§5.1.2)
    " an unboxing conversion (§5.1.8)

    "Numeric promotions are used to convert the operands of a numeric
    operator to a common type so that an operation can be performed.
    The two kinds of numeric promotion are unary numeric promotion
    (§5.6.1) and binary numeric promotion (§5.6.2)."

    So, by those sections you can see that the division must be evaluated
    as 'float'.

    For those who decry the use of the JLS to learn this, just note that the
    relevant sections are not especially obscure and they answer the
    question completely and authoritatively. But feel free to struggle with
    alternatives if you really want to work harder.

    <http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html>
    <http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.7>
    <http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.6>
    <http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.6.2>

    --
    Lew
     
    Lew, Jul 24, 2012
    #3
  4. On Tue, 24 Jul 2012 13:01:11 -0700, markspace wrote:

    > On 7/24/2012 12:57 PM, bob smith wrote:
    >> I can never remember this.
    >>
    >> Let's say you have an integer and a float in an operation. Is the
    >> result always a float?

    >
    >
    > You can just try this to see what you get, or read the JLS. From
    > memory, I'm 90% sure that ints will be promoted to floats. I'm not sure
    > how order of operations affects this. In the expression (1+1)/2.0f,
    > does the addition use floats or ints? I'm not sure, but I think ints.


    I think this:

    $ cat MathTest.java
    public class MathTest
    {
    public static void main(String[] args)
    {
    double x = (9 / 2) / 5;
    System.out.println("x = " + x);
    double y = (9 / 2) / 5.0;
    System.out.println("y = " + y);
    double z = (9 / 2.0) / 5.0;
    System.out.println("z = " + z);
    }
    }
    $ javac MathTest.java
    $ java MathTest
    x = 0.0
    y = 0.8
    z = 0.9


    shows pretty conclusively that widening from int to double isn't done
    until the last possible moment.

    The calculation of x is entirely integral, with widening to double only
    occurring at the assignment. Calculating y can only produce that result
    if the first division was integral and its result was then widened to
    double before the second division. And, of course, the z calculation was
    entirely done as floating point


    --
    martin@ | Martin Gregorie
    gregorie. | Essex, UK
    org |
     
    Martin Gregorie, Jul 24, 2012
    #4
  5. On Tue, 24 Jul 2012 13:21:33 -0700 (PDT), Lew <>
    wrote:

    [snip]

    >So, yes, the parenthesized addition is done as an 'int' addition.
    >
    >"5.6. Numeric Promotions
    >
    >"Numeric promotion is applied to the operands of an arithmetic operator.
    >Numeric promotion contexts allow the use of:
    >
    >" an identity conversion (§5.1.1)
    >" a widening primitive conversion (§5.1.2)
    >" an unboxing conversion (§5.1.8)
    >
    >"Numeric promotions are used to convert the operands of a numeric
    >operator to a common type so that an operation can be performed.
    >The two kinds of numeric promotion are unary numeric promotion
    >(§5.6.1) and binary numeric promotion (§5.6.2)."
    >
    >So, by those sections you can see that the division must be evaluated
    >as 'float'.
    >
    >For those who decry the use of the JLS to learn this, just note that the
    >relevant sections are not especially obscure and they answer the
    >question completely and authoritatively. But feel free to struggle with
    >alternatives if you really want to work harder.


    This sort of thing is handled in many introductory programming
    language texts so it is not harder at all to use them instead.

    ><http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html>
    ><http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.7>
    ><http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.6>
    ><http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.6.2>


    Whereas in a text, it might be "Chapter 3: Datatypes and
    Operations". A bit simpler, no?

    Sincerely,

    Gene Wirchenko
     
    Gene Wirchenko, Jul 24, 2012
    #5
  6. Patricia Shanahan <> writes:
    > On 7/24/2012 12:57 PM, bob smith wrote:


    >> Let's say you have an integer and a float in an operation. Is the


    > May I ask why you are using float? Because of its very limited
    > precision, it is better to use double unless there is a specific reason


    ...and even better to use BigDecimal, if you need all the decimals to be
    correct, like when calculating any amounts of money.

    Of course, there are situations where rounding errors don't matter and
    double is good enough.
    Like, I suppose, some statistical calculations.

    --
    Jukka Lahtinen
     
    Jukka Lahtinen, Jul 25, 2012
    #6
  7. bob smith

    Lew Guest

    Gene Wirchenko wrote:
    > Lew wrote:
    >
    > [snip]
    >
    >> So, yes, the parenthesized addition is done as an 'int' addition.
    >>
    >> "5.6. Numeric Promotions
    >>
    >> "Numeric promotion is applied to the operands of an arithmetic operator.
    >> Numeric promotion contexts allow the use of:
    >>
    >> " an identity conversion (§5.1.1)
    >> " a widening primitive conversion (§5.1.2)
    >> " an unboxing conversion (§5.1.8)
    >>
    >> "Numeric promotions are used to convert the operands of a numeric
    >> operator to a common type so that an operation can be performed.
    >> The two kinds of numeric promotion are unary numeric promotion
    >> (§5.6.1) and binary numeric promotion (§5.6.2)."
    >>
    >> So, by those sections you can see that the division must be evaluated
    >> as 'float'.
    >>
    >> For those who decry the use of the JLS to learn this, just note that the
    >> relevant sections are not especially obscure and they answer the
    >> question completely and authoritatively. But feel free to struggle with
    >> alternatives if you really want to work harder.

    >
    > This sort of thing is handled in many introductory programming
    > language texts so it is not harder at all to use them instead.
    >
    >> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html>
    >> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.7>
    >> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.6>
    >> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.6.2>

    >
    > Whereas in a text, it might be "Chapter 3: Datatypes and
    > Operations". A bit simpler, no?


    No.

    One place to find all the answers, authoritative and final. Versus many places
    of dubious quality that might at best indirectly hint at the answer. Victory: JLS.

    But you have a bug up your arse about the JLS and I recognize that from your
    continued efforts to speak against its use.

    I don't demand that anyone read the JLS. I just point out that it has the
    answers, that for the most part it's readable and that the more obscure parts
    are amenable to study, and that it's worthwhile. Those who excoriate its use,
    as opposed to, say, recommending that one work with additional material as
    well, are leading the rest astray. I really don't understand this rabid
    rejection of such a useful resource.

    Those of you without an irrational fear of the JLS should judge for
    yourselves. Don't be afraid of it because the Genes of the world are trying to
    frighten you away from its use. Oh, don't use it as your only source, not even
    after you've gained familiarity with it and with Java, but by all means use
    it. Gene is wrong to discourage that.

    --
    Lew
    Honi soit qui mal y pense.
    http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg
     
    Lew, Jul 25, 2012
    #7
  8. bob smith

    Arne Vajhøj Guest

    On 7/25/2012 5:22 AM, Jukka Lahtinen wrote:
    > Patricia Shanahan <> writes:
    >> On 7/24/2012 12:57 PM, bob smith wrote:

    >
    >>> Let's say you have an integer and a float in an operation. Is the

    >
    >> May I ask why you are using float? Because of its very limited
    >> precision, it is better to use double unless there is a specific reason

    >
    > ..and even better to use BigDecimal, if you need all the decimals to be
    > correct, like when calculating any amounts of money.
    >
    > Of course, there are situations where rounding errors don't matter and
    > double is good enough.
    > Like, I suppose, some statistical calculations.


    Anything that is measured with uncertainty.

    Arne
     
    Arne Vajhøj, Jul 25, 2012
    #8
  9. On Wed, 25 Jul 2012 06:33:24 -0700, Lew <> wrote:

    >Gene Wirchenko wrote:
    >> Lew wrote:


    [snip]

    >>> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html>
    >>> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.7>
    >>> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.6>
    >>> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.6.2>

    >>
    >> Whereas in a text, it might be "Chapter 3: Datatypes and
    >> Operations". A bit simpler, no?

    >
    >No.
    >
    >One place to find all the answers, authoritative and final. Versus many places
    >of dubious quality that might at best indirectly hint at the answer. Victory: JLS.


    Authoritative and final:
    "One Ring to rule them all
    And in the Darkness bind them."

    >But you have a bug up your arse about the JLS and I recognize that from your
    >continued efforts to speak against its use.


    Actually, you do.

    Perish the thought that someone starting in Java might not find
    the JLS all that readable. Perish the thought that someone might be
    able to explain something better than is done in the JLS.

    You prevaricate very well. (prevaricate: to selectively tell the
    truth in order to mislead) I suggest that a Java newbie start with an
    introductory text and use the JLS later.

    >I don't demand that anyone read the JLS. I just point out that it has the
    >answers, that for the most part it's readable and that the more obscure parts
    >are amenable to study, and that it's worthwhile. Those who excoriate its use,
    >as opposed to, say, recommending that one work with additional material as
    >well, are leading the rest astray. I really don't understand this rabid
    >rejection of such a useful resource.


    But we do not reject it. By stating that we do, you get to score
    points. That sort of behaviour has gotten old.

    >Those of you without an irrational fear of the JLS should judge for
    >yourselves. Don't be afraid of it because the Genes of the world are trying to
    >frighten you away from its use. Oh, don't use it as your only source, not even
    >after you've gained familiarity with it and with Java, but by all means use
    >it. Gene is wrong to discourage that.


    Again, I do not do that.

    Lew, why do you keep turning things into unpleasant arguments?
    There is a big difference between disagreeing and being disagreeable.
    How about trying the former for a change?

    Sincerely,

    Gene Wirchenko
     
    Gene Wirchenko, Jul 25, 2012
    #9
  10. bob smith

    Roedy Green Guest

    On Wed, 25 Jul 2012 12:22:02 +0300, Jukka Lahtinen
    <> wrote, quoted or indirectly quoted
    someone who said :

    >Of course, there are situations where rounding errors don't matter and
    >double is good enough.
    >Like, I suppose, some statistical calculations.


    If something represents a measurement, e.g. the length of a desk, then
    double will nearly always suffice. When doing math on fat integers,
    like computing pi, or doing encryption then you want BigInteger
    --
    Roedy Green Canadian Mind Products
    http://mindprod.com
    The greatest shortcoming of the human race is our inability to understand the exponential function.
    ~ Dr. Albert A. Bartlett (born: 1923-03-21 age: 89)
    http://www.youtube.com/watch?v=F-QA2rkpBSY
     
    Roedy Green, Jul 25, 2012
    #10
  11. bob smith

    Lew Guest

    Gene Wirchenko wrote:
    > Lew wrote:
    >> Perish the thought that someone starting in Java might not find
    >> the JLS all that readable. Perish the thought that someone might be
    >> able to explain something better than is done in the JLS.

    >
    > You prevaricate very well. (prevaricate: to selectively tell the
    > truth in order to mislead) I suggest that a Java newbie start with an
    > introductory text and use the JLS later.


    I never said a newbie should avoid introductory texts. Nor do I suggest
    that a newbie rely on the JLS. You have misunderstood my points yet again.

    I agree that introductory texts are great to introduce Java.

    My objection is to the active discouragement of the use of the JLS.

    I recommend that newbies be aware of the JLS and practice reading
    it from an early age. That is not so inconsistent with your recommendation.

    As for calling me a liar, screw you.

    > &gt;I don't demand that anyone read the JLS. I just point out that it has the
    > &gt;answers, that for the most part it's readable and that the more obscure parts
    > &gt;are amenable to study, and that it's worthwhile. Those who excoriate its use,
    > &gt;as opposed to, say, recommending that one work with additional material as
    > &gt;well, are leading the rest astray. I really don't understand this rabid
    > &gt;rejection of such a useful resource.
    >
    > But we do not reject it. By stating that we do, you get to score
    > points. That sort of behaviour has gotten old.


    But you have rejected it, repeatedly.

    >
    > &gt;Those of you without an irrational fear of the JLS should judge for
    > &gt;yourselves. Don't be afraid of it because the Genes of the world are trying to
    > &gt;frighten you away from its use. Oh, don't use it as your only source, not even
    > &gt;after you've gained familiarity with it and with Java, but by all means use
    > &gt;it. Gene is wrong to discourage that.
    >
    > Again, I do not do that.
    >
    > Lew, why do you keep turning things into unpleasant arguments?
    > There is a big difference between disagreeing and being disagreeable.
    > How about trying the former for a change?


    How about you stop trying to frighten folks away from the JLS?

    If you agree with me that it's a valuable resource of which to be aware,
    and that one should aspire to its use eventually, then why do you argue
    with me?

    It is you who resorts to name calling and unpleasantness. It is a raw
    tactic for you to accuse me of being "disagreeable" because you don't
    agree that the JLS is a valuable resource. I am disagreeing so adamantly
    because your continued speech against it is likely to discourage those
    who would most benefit from it. You are performing a disservice to the
    Java community, and when called on it, resort to name-calling and
    ad hominem attacks.

    I am only suggesting a balanced approach wherein from the very
    start a Java programmer is aware of the definitive definition of
    the language, and of the value of being able to use it. I am astounded
    that anyone finds that objectionable, much less resorts to the sort
    of underhanded responses in which you engaged.

    --
    Lew
     
    Lew, Jul 26, 2012
    #11
  12. On Wed, 25 Jul 2012 17:09:27 -0700 (PDT), Lew <>
    wrote:

    >Gene Wirchenko wrote:
    >> Lew wrote:
    >>> Perish the thought that someone starting in Java might not find
    >>> the JLS all that readable. Perish the thought that someone might be
    >>> able to explain something better than is done in the JLS.

    >>
    >> You prevaricate very well. (prevaricate: to selectively tell the
    >> truth in order to mislead) I suggest that a Java newbie start with an
    >> introductory text and use the JLS later.

    >
    >I never said a newbie should avoid introductory texts. Nor do I suggest
    >that a newbie rely on the JLS. You have misunderstood my points yet again.
    >
    >I agree that introductory texts are great to introduce Java.


    Do you agree that intro texts are not the JLS?

    >My objection is to the active discouragement of the use of the JLS.


    So which is it? When I state that a newbie should go with intro
    texts, I am stating how a newbie should be introduced to Java. The
    JLS can come later.

    >I recommend that newbies be aware of the JLS and practice reading
    >it from an early age. That is not so inconsistent with your recommendation.


    No, it is not. I just think that starting with it will cause
    more trouble than it is worth.

    >As for calling me a liar, screw you.


    This is typical. I did not call you a liar. I stated that you
    prevaricate. Again, prevaricate: to selectively tell the truth in
    order to mislead.

    >> &gt;I don't demand that anyone read the JLS. I just point out that it has the
    >> &gt;answers, that for the most part it's readable and that the more obscure parts
    >> &gt;are amenable to study, and that it's worthwhile. Those who excoriate its use,
    >> &gt;as opposed to, say, recommending that one work with additional material as
    >> &gt;well, are leading the rest astray. I really don't understand this rabid
    >> &gt;rejection of such a useful resource.
    >>
    >> But we do not reject it. By stating that we do, you get to score
    >> points. That sort of behaviour has gotten old.

    >
    >But you have rejected it, repeatedly.


    Only for someone just starting out.

    >> &gt;Those of you without an irrational fear of the JLS should judge for
    >> &gt;yourselves. Don't be afraid of it because the Genes of the world are trying to
    >> &gt;frighten you away from its use. Oh, don't use it as your only source, not even
    >> &gt;after you've gained familiarity with it and with Java, but by all means use
    >> &gt;it. Gene is wrong to discourage that.
    >>
    >> Again, I do not do that.
    >>
    >> Lew, why do you keep turning things into unpleasant arguments?
    >> There is a big difference between disagreeing and being disagreeable.
    >> How about trying the former for a change?

    >
    >How about you stop trying to frighten folks away from the JLS?


    I do not. I just suggest later, after the intro texts.

    >If you agree with me that it's a valuable resource of which to be aware,
    >and that one should aspire to its use eventually, then why do you argue
    >with me?


    That is odd. *I* am the one who keeps stating eventually, and
    you keep giving me trouble over it.

    >It is you who resorts to name calling and unpleasantness. It is a raw
    >tactic for you to accuse me of being "disagreeable" because you don't
    >agree that the JLS is a valuable resource. I am disagreeing so adamantly
    >because your continued speech against it is likely to discourage those
    >who would most benefit from it. You are performing a disservice to the
    >Java community, and when called on it, resort to name-calling and
    >ad hominem attacks.


    "disagreeing adamantly" is often disagreeable. Stating that I
    have "an irrational fear of the JLS" is name-calling on your part.

    >I am only suggesting a balanced approach wherein from the very
    >start a Java programmer is aware of the definitive definition of
    >the language, and of the value of being able to use it. I am astounded
    >that anyone finds that objectionable, much less resorts to the sort
    >of underhanded responses in which you engaged.


    Prevarication is underhanded, and you have been busy doing it.

    I have consistently stated that a newbie should wait on using the
    JLS. I have never stated that it should not be used.

    Sincerely,

    Gene Wirchenko
     
    Gene Wirchenko, Jul 26, 2012
    #12
  13. On 7/25/2012 9:33 AM, Lew wrote:
    > Gene Wirchenko wrote:
    >> Lew wrote:
    >>> For those who decry the use of the JLS to learn this, just note that the
    >>> relevant sections are not especially obscure and they answer the
    >>> question completely and authoritatively. But feel free to struggle with
    >>> alternatives if you really want to work harder.

    >>
    >> This sort of thing is handled in many introductory programming
    >> language texts so it is not harder at all to use them instead.
    >>
    >>> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html>
    >>> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.7>
    >>> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.6>
    >>> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.6.2>

    >>
    >> Whereas in a text, it might be "Chapter 3: Datatypes and
    >> Operations". A bit simpler, no?

    >
    > No.
    >
    > One place to find all the answers, authoritative and final. Versus many
    > places of dubious quality that might at best indirectly hint at the
    > answer. Victory: JLS.


    "authoritative and final" does not imply "not harder" or "simpler".

    JLS is by definition the authoritative source and should be consulted
    if there are doubt in other sources or implementations.

    But it does not mean that a Java beginners guide can not have an easier
    to read explanation.

    Arne
     
    Arne Vajhøj, Jul 26, 2012
    #13
  14. bob smith

    Jan Burse Guest

    Hi,

    Gene Wirchenko schrieb:
    >> You are performing a disservice to the
    >> >Java community, and when called on it, resort to name-calling and
    >> >ad hominem attacks.

    > "disagreeing adamantly" is often disagreeable. Stating that I
    > have "an irrational fear of the JLS" is name-calling on your part.
    >


    3rd time I observe this already on c.l.j.p today,
    troll against troll. It could be only that it is
    summertime, and everybody is on the beach except
    for the trolls (and me having back pain).

    Ha Ha. Nearly makes my day.

    Bye
     
    Jan Burse, Jul 26, 2012
    #14
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