Compact Number Formatting and Fraction Digits

Gunnar Morling gunnar at
Thu Jan 17 17:42:26 UTC 2019

> this could be a good value add to introduce an API [...]

Should I file a JDK issue then (not sure I can even)?

> Wouldn’t this be accomplished with setMaximumFractionDigits(1) ?

That wouldn't achieve that there's no fraction digit(s) in case of
trailing 0s. With min and max fraction digits set to 1, there'll
always be exactly one fraction digit. So having an API that'd allow to
remove trailing 0s would be very welcomed.

Btw. another suggestion I'd have is to document guarantees in terms of
thread-safety of CompactNumberFormat. It's a common mistake to use
SimpleDateFormat concurrently from multiple threads (although its docs
even state that this is incorrect). So CNF should at least document
its behaviour (or even allow for concurrent access, if feasible).

Am Do., 17. Jan. 2019 um 15:50 Uhr schrieb Scott Palmer <swpalmer at>:
> Wouldn’t this be accomplished with setMaximumFractionDigits(1) ?
> > On Jan 17, 2019, at 5:13 AM, Nishit Jain <nishit.jain at> wrote:
> >
> > Hi Gunnar,
> >
> > Currently there is no way to obtain the below expected behavior (to get 1K) when min fraction digit is set to non-zero value. I think that is not even expected when min fraction digits is set, but considering the objective of compact number formatting this could be a good value add to introduce an API which if set, truncates trailing fractional zeros while formatting output. This may need some thought process on its feasibility.
> >
> > Regards,
> > Nishit Jain
> > On 17-01-2019 14:37, Gunnar Morling wrote:
> >> Hi,
> >>
> >> I took a look at the compact number formatting recently added in JDK 12.
> >>
> >> There's setMinimumFractionDigits() to control the number of fractional
> >> digits, so that e.g. 1,500 can be formatted as 1.5K. That's great, but
> >> it also will format 1,000 as 1.0K. Is there a way to have fractional
> >> digits but remove trailing zeros, so that 1,500 and 1,000 would be
> >> formatted as 1.5K and 1K, respectively?

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