Formatting Double to String?

Question

String.format("%,.0f", 200000000000000000000000.0)

-> 199,999,999,999,999,980,000,000 why?

Because of the precision of the internal representation. See [Is floating point math broken?](https://stackoverflow.com/questions/588004/is-floating-point-math-broken?r=SearchResults) — lurker, Oct 07 '19 at 10:10
@LongNguyenVan you may look here for solution: https://stackoverflow.com/questions/48201462/store-big-price-value-in-database-along-with-decimal-point-in-sqlite-database — Bhoomika Patel, Oct 07 '19 at 10:12

score 0 · Answer 1 · answered Oct 07 '19 at 10:09

Understand the Double Data type - it is an approximation of amount and scale.

The Following assignment:

double d = 2.00000000000f;

will generate a value of 1.9999999 at times when printed. What you are seeing here is magnification of that. Double Data types also have a maximum (implementation-dependant) of how many places of significance they can support (upto 15 generally) - which is why the last 6 digits are all zeros (0)

For your particular solution, if you don't require Floating-point Data, stick to Integer.

but when i tried it, it was scaled with 21 zeros(0) – Long Nguyen Van Oct 07 '19 at 10:20 — Long Nguyen Van, Oct 07 '19 at 10:20

score 0 · Answer 2 · answered Oct 07 '19 at 10:25

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It is because current processors(and most VMs) work like that if use default data types. Here it is explained in details

If you want precision use BigDecimal. This class is specifically intended for situations like this - to be used in currency related stuff and scientific calculations.

To format decimals in proper way Java has DecimalFormat

String pattern = "###,###.###";
DecimalFormat decimalFormat = new DecimalFormat(pattern);

String format = decimalFormat.format(123456789.123);
System.out.println(format); // -> 123.456.789,123

Here is nice tutorial about it

Hope it helps.

answered Oct 07 '19 at 10:25

Pavlo Ostasha

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still be with value 200000000000000000000000.0 – Long Nguyen Van Oct 07 '19 at 10:28
@LongNguyenVan with DecimalFormat - yes because if uses the same double as you - I showed it just to show how to format decimals correct in java. Use BigDecimal for giant numbers - you have control over rounding using this class. – Pavlo Ostasha Oct 07 '19 at 11:04
thanks Use BigDecimal and MathContext – Long Nguyen Van Oct 08 '19 at 01:41
@Long Nguyen Van please accept answer if it is correct – Pavlo Ostasha Oct 08 '19 at 06:18

score 0 · Accepted Answer · answered Oct 08 '19 at 01:43

0

My problem has been solved

String.format("%,.0f", BigDecimal( 200000000000000000000000.0, MathContext.DECIMAL64))

answered Oct 08 '19 at 01:43

Long Nguyen Van

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Formatting Double to String?

3 Answers3