DecimalFormat is not working properly

Question

I am trying to apply formatting (, after 3 digits and rounding after 4 digits), using below code -

double a = 1231254125412512.231515235346;
NumberFormat formatter = new DecimalFormat("#,###");
formatter.setRoundingMode(RoundingMode.HALF_UP);
formatter.setMinimumFractionDigits(4);
formatter.setMaximumFractionDigits(4);
System.out.println("Number : " + formatter.format(a));

Above code is working properly for the number -54125412512.231515235346 (result was -54,125,412,512.2315).

But it is not working for the number -1231254125412512.231515235346 (result -1,231,254,125,412,512.2000).

Because Double has a precision of 53 bit. So its maximum is 17 digits. 1231254125412512.231515235346 ~ 1231254125412512.2 (17 digits) — ThiepLV, Jun 28 '16 at 09:08

score 2 · Answer 1 · answered Jun 28 '16 at 08:34

2

Double has a precision of 53 bit which is about 16 digits.

answered Jun 28 '16 at 08:34

J Fabian Meier

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score 1 · Accepted Answer · edited May 23 '17 at 10:30

1

Problem is you use double variable, and and hit max precision ~~Double.MIN_VALUE~~.

SOURCE:

double: 64 bits (8 bytes) where 52 bits are used for the mantissa (15 to 17 decimal digits, about 16 on average). 11 bits are used for the exponent and 1 bit is the sign bit.

To avoid this problem use BigDecimal instead:

BigDecimal a = new BigDecimal("-54125412512.231515235346");
BigDecimal b = new BigDecimal("-1231254125412512.231515235346");

NumberFormat formatter = new DecimalFormat("#,###");
formatter.setRoundingMode(RoundingMode.HALF_UP);
formatter.setMinimumFractionDigits(4);
formatter.setMaximumFractionDigits(4);
System.out.println("Number : " + formatter.format(a));
System.out.println("Number : " + formatter.format(b));

OUTPUT:

Number : -54.125.412.512,2315
Number : -1.231.254.125.412.512,2315

edited May 23 '17 at 10:30

Community

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answered Jun 28 '16 at 08:34

Jordi Castilla

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8
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109

1

Your solution is correct, but your first statement is not. 1231254125412512.231515235346 < Double.MAX_VALUE and (-1231254125412512.231515235346) > Double.MIN_VALUE. The problems is that a double doesn't have the precision to hold a number that is so large and has so much precision so it will be rounded. – Erwin Bolwidt Jun 28 '16 at 08:36
@ErwinBolwidt corrected and linked a source. thanks a lot! – Jordi Castilla Jun 28 '16 at 08:40

DecimalFormat is not working properly

2 Answers2