Format a number with leading sign

问题:

How do I format in Java a number with its leading sign?

Negative numbers are correctly displayed with leading -, but obviously positive numbers are not displayed with +.

How to do that in Java? My current currency format string is \#\#\#,\#\#\#,\#\#\#,\#\#\#,\#\#0.00 (yes, I need to format positive/negative currency values)

回答1:

Use a negative subpattern, as described in the javadoc for DecimalFormat.

DecimalFormat fmt = new DecimalFormat("+#,##0.00;-#");
System.out.println(fmt.format(98787654.897));
System.out.println(fmt.format(-98787654.897));

produces (in my French locale where space is the grouping separator and the comma is the decimal separator) :

+98 787 654,90
-98 787 654,90

回答2:

API for Formatter provides an example:

Formatter formatter = new Formatter();
System.out.println(formatter.format(Locale.FRANCE, "e = %+10.4f", Math.E));
//e =    +2,7183

回答3:

I did:

private NumberFormat plusMinusNF = new DecimalFormat("+#;-#");

Integer newBalance = (Integer) binds.get("newBalance");
bindsForUpdate.put("plusMinus", plusMinusNF.format(newBalance));

which formatted positive integers, e.g. 5 to "+5" and negative integers, e.g -7 to "-7" (as expected)

回答4:

It requires a little tweaking of the DecimalFormat returned by NumberFormat.getCurrencyInstance() to do it in a locale-independent manner. Here's what I did (tested on Android):

DecimalFormat formatter = (DecimalFormat)NumberFormat.getCurrencyInstance();
String symbol = formatter.getCurrency().getSymbol();
formatter.setNegativePrefix(symbol+"-");
// or "-"+symbol if that's what you need
formatter.setNegativeSuffix("");

IIRC, Currency.getSymbol() may not return a value for all locales for all systems, but it should work for the major ones (and I think it has a reasonable fallback on its own, so you shouldn't have to do anything)

ageektrapped

Source: Format negative amount of USD with a minus sign, not brackets (Java)