java.text.DecimalFormat blank when zero?

Question

Is it possible to show blank (empty string) when the number is zero (0)? (strict no zeros at left)

Answer 1

You may be able to use MessageFormat, specifically its ChoiceFormat feature:

double[] nums = {
    -876.123, -0.1, 0, +.5, 100, 123.45678,
};
for (double num : nums) {
    System.out.println(
        num + " " +
        MessageFormat.format(
            "{0,choice,-1#negative|0#zero|0<{0,number,'#,#0.000'}}", num
        )
    );
}

This prints:

-876.123 negative
-0.1 negative
0.0 zero
0.5 0.500
100.0 1,00.000
123.45678 1,23.457

Note that MessageFormat does use a DecimalFormat under the hood. From the documentation:

FORMAT TYPE:       number
FORMAT STYLE:      subformatPattern
SUBFORMAT CREATED: new DecimalFormat(
                      subformatPattern,
                      DecimalFormatSymbols.getInstance(getLocale())
                   )

So this does use a DecimalFormat, albeit indirectly. If this, for some reason, is forbidden, then you must resort to checking for a special condition yourself, since DecimalFormat does not distinguish zero. From the documentation:

DecimalFormat patterns have the following syntax:

 Pattern:
         PositivePattern
         PositivePattern ; NegativePattern

There is no option to provide a special pattern for zero, so there is no DecimalFormat pattern that can do this for you. You can either have, say, an if-check, or just let MessageFormat/ChoiceFormat do it for you as shown above.