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From: =?UTF-8?Q?Arne_Vajh=c3=b8j?= <arne@vajhoej.dk>
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Subject: Re: [OT] Re: missing import java.lang.Comparable
Date: Mon, 11 Jul 2016 22:13:39 -0400
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On 7/11/2016 8:30 AM, Eric Douglas wrote:
> On Friday, July 8, 2016 at 8:32:14 PM UTC-4, Arne Vajhøj wrote:
>> I don't think this example shows what you think it shows.
>>
>> It really shows that String.valueOf has an impact on the result.
>
> Converting to a String is what makes it work.

String.valueOf "round off" a little bit in the string result.

But I would not consider that a general solution.

> Whether it's the financial application dealing with fractions of
> pennies or an inventory management application which may have
> fractions depending on the unit of measure, I expect .0001 + .0002 to
> get exactly .0003.

Then you better use a data type that has this characteristic.

Use BigDecimal not double.



>
> Code:
>    DecimalFormat myFormatter = new DecimalFormat("0.####################");
>    String output;
>    double a = .0002;
>    double b = .0001;
>    output = myFormatter.format(a + b);
>    System.out.println(output);
>    BigDecimal bda = new BigDecimal(String.valueOf(a));
>    BigDecimal bdb = new BigDecimal(String.valueOf(b));
>    bda = bda.add(bdb);
>    output = myFormatter.format(bda.doubleValue());
>    System.out.println(output);
> Output:
> 0.00030000000000000003
> 0.0003
>
> Code:
>    DecimalFormat myFormatter = new DecimalFormat("0.####################");
>    String output;
>    double a = .0002;
>    double b = .0001;
>    output = myFormatter.format(a + b);
>    System.out.println(output);
>    BigDecimal bda = new BigDecimal(a);
>    BigDecimal bdb = new BigDecimal(b);
>    bda = bda.add(bdb);
>    output = myFormatter.format(bda.doubleValue());
>    System.out.println(output);
> Output:
> 0.00030000000000000003
> 0.00030000000000000003

Yes. But I think you want to do this:

	    DecimalFormat fmt = new DecimalFormat("0.####################");
	    BigDecimal bda = new BigDecimal("0.0002");
	    BigDecimal bdb = new BigDecimal("0.0001");
	    BigDecimal bdc = bda.add(bdb);
	    System.out.println(bdc);
	    System.out.println(fmt.format(bdc));

0.0003
0.0003

Arne