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Thread: working with BigDecimal and MathContext

  1. #1
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    Default working with BigDecimal and MathContext

    Hi Every body!!


    I'm learning java this semester, I have a C/C++ background so sometimes things get a litter bit confusing in here, hopefully I learn the very basis soon :-)


    I'm working with a method that accept a double without format, it might looks something like this 14564852.51654874659765456874684639786514356452364 or 784643213218432516548468486.3 and the method must forma it to a two decimal number rounding it up (14564852.52 or 784643213218432516548468486.30)

    this is how I code this method


     public double formatMoney(double money) {
            double money_formatted = 0.00;
     
            if (money >= 0) {
                BigDecimal formatted_1 = new BigDecimal(money);
                MathContext format = new MathContext(2, RoundingMode.CEILING);
                formatted_1.round(format);            
                money_formatted = formatted_1.doubleValue();
                System.out.println(formatted_1);//<-----------------in here I'm getting a big number that I don't know where come from
            }
     
            return money_formatted;
        }


    I'll appreciate any input that any of you can give me!


    have a nice day!


  2. #2
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    Default Re: working with BigDecimal and MathContext

    What are you doing with the value returned by the round() method?

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    Default Re: working with BigDecimal and MathContext

    I thought the round method modify "this" BigDecimal object, but I'm not sure if I'm doing it correctly, do you know how I should do it????

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    Default Re: working with BigDecimal and MathContext

    Did you try using the value returned by the round() method?

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    Default Re: working with BigDecimal and MathContext

    I just checked it, it returns a BigDecimal object,

    should this work?(I added another BigDecimal object called formatted_2)

     public double formatMoney(double money) {
            double money_formatted = 0.00;
     
            if (money >= 0) {
                BigDecimal formatted_1 = new BigDecimal(money);
                BigDecimal formatted_2;
                MathContext format = new MathContext(2, RoundingMode.CEILING);
                formatted_2 = formatted_1.round(format);            
                money_formatted = formatted_2.doubleValue();
                System.out.println(formatted_1);//<-----------------in here I'm getting a big number that I don't know where come from
            }
     
            return money_formatted;
        }

    thanks again for your inputs


    PS: I don't have my code with me to test it right now :-(

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    Default Re: working with BigDecimal and MathContext

    should this work?
    The javac and java programs should answer that for you.

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    Default Re: working with BigDecimal and MathContext

    Quote Originally Posted by Norm View Post
    The javac and java programs should answer that for you.
    it compiles and runs, but doesn't behave I would like to.

    the output that I'm getting is 1500.0 when I introduce 1452.78965412 and I want to get 1452.79,

    what am I doing wrong?

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    Default Re: working with BigDecimal and MathContext

    Try looking at the round(). It's rounding to the 10th decimal place.

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    Default Re: working with BigDecimal and MathContext

    Quote Originally Posted by Mr.777 View Post
    Try looking at the round(). It's rounding to the 10th decimal place.
    round() returns this 1.5E+3.

    I think the error is in this line

    MathContext format = new MathContext(2, RoundingMode.HALF_UP);

    how should I set it? in order to get 1452.79 (only two decimals)

  10. #10
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    Default Re: working with BigDecimal and MathContext

    Try some of the other methods of the BigDecimal class. I'm sure one of them will do what you want.

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    Default Re: working with BigDecimal and MathContext

    I don't see any other method that can help me :-( , I'm using this site

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    Default Re: working with BigDecimal and MathContext

    What do the scale methods do?

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    Default Re: working with BigDecimal and MathContext

    well, I couldn't (or at least I haven't learn) use scale() method, instead I use setscale() method

     
    public double formatMoney(double money) {
            double money_formatted = 0.00;
     
            if (money >= 0) {
                String dvalue = Double.toString(money);
                BigDecimal bd = new BigDecimal(dvalue, MathContext.UNLIMITED);  //creo que es un poco duro, pero deberķa funcionar
                BigDecimal bd2;
                bd2 = bd.setScale(2, RoundingMode.HALF_UP);
                money_formatted = bd2.doubleValue();       
            }
     
            return money_formatted;
        }


    however this method works fine with any double except those ends by .00

    I introduces 25.00 and then I got 25.0 and I want 25.00 :-(

  14. #14
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    Default Re: working with BigDecimal and MathContext

    Did you try different rounding modes?

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    Default Re: working with BigDecimal and MathContext

    I used FLOOR, CEILING, UP, DOWN, HALF_UP, HALF_DOWN and all gave me the same result

  16. #16
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    Default Re: working with BigDecimal and MathContext

    That's strange. When I ran it I get the following from different tests:

    System.out.println("f1="+formatted_1 + " f2="+formatted_2 +", mf="+ money_formatted);
    //f1=1452.789654120000022885506041347980499267578125 f2=1.5E+3, mf=1500.0 <<<< round()
    //f1=1452.789654120000022885506041347980499267578125 f2=1452.79, mf=1452.79
    //f1=1452.789654120000022885506041347980499267578125 f2=1452.7897, mf=1452.7897

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    Default Re: working with BigDecimal and MathContext

    it is strange, because I get more desirable results this is the code that I'm using right now

    public double formatMoney(double money) {
            double money_formatted = 0.00;
     
            if (money >= 0) {
                String dvalue = Double.toString(money);
                BigDecimal bd = new BigDecimal(dvalue, MathContext.UNLIMITED);  //creo que es un poco duro, pero deberķa funcionar
                BigDecimal bd2;
                bd2 = bd.setScale(2, RoundingMode.HALF_UP);
                money_formatted = bd2.doubleValue();       
            }
     
            return money_formatted;
        }

  18. #18
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    Default Re: working with BigDecimal and MathContext

    I have no answers other than try different combinations of methods and values until you get the one you want.

  19. #19
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    Default Re: working with BigDecimal and MathContext

    ok, thanks very much for trying! :-)

  20. #20
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    Default Re: working with BigDecimal and MathContext

    You're welcome.

  21. #21
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    Default Re: working with BigDecimal and MathContext

    I just learned Java doesn't like 0.00, so it change it to 0.0 so the method works just fine

  22. #22
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    Default Re: working with BigDecimal and MathContext

    No, you can still use format() to format the Double like 0.00.
    Read through the API Docs once again.

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