Thread: 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!

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

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????

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

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 :-(

should this work?

The javac and java programs should answer that for you.

Originally Posted by Norm

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?

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

Originally Posted by Mr.777

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)

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

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

What do the scale methods do?

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 debería 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 :-(

Did you try different rounding modes?

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

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

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 debería funcionar
            BigDecimal bd2;
            bd2 = bd.setScale(2, RoundingMode.HALF_UP);
            money_formatted = bd2.doubleValue();       
        }
 
        return money_formatted;
    }

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

ok, thanks very much for trying! :-)

You're welcome.

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

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