Is it possible to use String.format for a conditional decimal point?

问题

In java, is it possible to use String.format to only show a decimal if there is actually a need? For example, if I do this:

String.format("%.1f", amount);

it will format: "1.2222" -> "1.2" "1.000" -> "1.0" etc,

but in the second case (1.000) I want it to return just "1". Is this possible with String.format, or am going to have to use a DecimalFormatter?

If I have to use a decimal formatter, will I need to make a separate DecimalFormatter for each type of format I want? (up to 1 decimal place, up to 2 decimal places, etc)

回答1:

No, you have to use DecimalFormat:

final DecimalFormat f = new DecimalFormat("0.##");
System.out.println(f.format(1.3));
System.out.println(f.format(1.0));

Put as many #s as you'd like; the DecimalFormat will only print as many digits as it thinks are significant, up to the number of #s.

回答2:

This might get you what your looking for; I'm not sure of the requirements or context of your request.

float f;
f = 1f
System.out.printf(f==Math.round(f) ? "%d\n" : "%s\n", f); //1
f = 1.555f
System.out.printf(f==Math.round(f) ? "%d\n" : "%s\n", f); //1.555

Worked great for what I needed.

FYI, above, System.out.printf(fmt, x) is like System.out.print(String.format(fmt, x)

来源：https://stackoverflow.com/questions/2164649/is-it-possible-to-use-string-format-for-a-conditional-decimal-point