DecimalFormat pattern

Question

public static String formatAmountUpToTwoDecimalNumber(String amount) { if(amount==null || "".equals(amount)) { return ""; } Double doubleAmount = Double.valueOf(amount); double myAmount = doubleAmount.doubleValue(); NumberFormat f = new DecimalFormat("###,###,###,###,##0.00"); String s = f.format(myAmount); return s; }

"###,###,###,###,##0.00", What exactly is the purpose of this pattern ? I believe it serves two purposes

to group numbers, that is put thousand seperator comma
to append two zeros after decimal if decimal is missing that is convert 23 to 23.00

But why there is "0" instead of "#" before decimal? what exactly is the purpose of this zero? Thanks for the help.

rray · Accepted Answer · 2014-04-30 11:14:39Z

21

Symbol Location Localized? Meaning 0 Number Yes Digit # Number Yes Digit, zero shows as absent

From: http://docs.oracle.com/javase/7/docs/api/java/text/DecimalFormat.html

So # is not shown when there is no number. The leading 0 means there will be at least 1 digit before the decimal separator.

edited Apr 30, 2014 at 11:14

rray

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answered Dec 14, 2011 at 10:34

Pieter

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6 Comments

Zohaib Over a year ago

thanks I looked at the documentation, but could not really understand. I was confused, should'nt zero be taken in its literal meaning ?

Pieter Over a year ago

As explained in the documentation, the zero should not be taken literal when used in a format string.

Zohaib Over a year ago

"There will be atleast 1 digit", do you want to say that if there was no digit before decimal that i if i pass .7, it will return me 0.70 after appending a leading zero ?

Andrew Thompson Over a year ago

+1, but please don't link to the docs. for an obsolete JRE. URL adjusted.

Pieter Over a year ago

Thanks Andrew. Hadn't noticed that.

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Sergey Kalinichenko · Accepted Answer · 2011-12-14 10:34:55Z

# will put a digit only if it is not a leading zero. 0 will put a digit even if it is a trailing zero. You could use zeros in front, too, if you wanted a fixed number of digits printed.

Dave Richardson · Accepted Answer · 2011-12-14 10:48:48Z

4

With the zero before the dp, small numbers like 0.23 will be displayed as 0.23. Without it you will not get the leading zero, so it is just displayed as .23. If you have a spreadsheet like excel you can check this there too.

answered Dec 14, 2011 at 10:48

Dave Richardson

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6 Comments

MikeB Over a year ago

I just tested this with ###.### and I get 0.23 which is quite annoying as I don't want the leading zero for what I'm doing

Dave Richardson Over a year ago

@MikeB - I just checked with Excel 2003 and the leading zero is definitely dropped if the cell formatting is ###.###

MikeB Over a year ago

@DaveRiz but this is a java question

Dave Richardson Over a year ago

@MikeB - yes, I know that - but the same principle applies in excel. I'm a java programmer, I use excel as a tool to illustrate the point.

MikeB Over a year ago

I believe java should be doing what Excel is doing but it appears to me that it's not. This test failed for me in java, : assertThat(new DecimalFormat("###.###").format(0.23d), is(".23"));

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