[英]Use DecimalFormat to get varying amount of decimal places
So I want to use the Decimal Format class to round numbers:所以我想使用 Decimal Format 类来舍入数字:
double value = 10.555;
DecimalFormat fmt = new DecimalFormat ("0.##");
System.out.println(fmt.format(value));
Here, the variable value
would be rounded to 2 decimal places, because there are two #
s.在这里,变量
value
将四舍五入到小数点后两位,因为有两个#
。 However, I want to round value
to an unknown amount of decimal places, indicated by a separate integer called numPlaces
.但是,我想将
value
四舍五入到未知数量的小数位,由一个名为numPlaces
的单独整数numPlaces
。 Is there a way I could accomplish this by using the Decimal Formatter?有没有办法通过使用十进制格式器来实现这一点?
eg If numPlaces = 3
and value = 10.555
, value
needs to be rounded to 3 decimal places例如,如果
numPlaces = 3
且value = 10.555
,则value
需要四舍五入到小数点后 3 位
Create a method to generate a certain number of #
to a string, like so:创建一个方法来为字符串生成一定数量的
#
,如下所示:
public static String generateNumberSigns(int n) {
String s = "";
for (int i = 0; i < n; i++) {
s += "#";
}
return s;
}
And then use that method to generate a string to pass to the DecimalFormat
class:然后使用该方法生成一个字符串以传递给
DecimalFormat
类:
double value = 1234.567890;
int numPlaces = 5;
String numberSigns = generateNumberSigns(numPlaces);
DecimalFormat fmt = new DecimalFormat ("0." + numberSigns);
System.out.println(fmt.format(value));
OR simply do it all at once without a method:或者只是在没有方法的情况下一次性完成:
double value = 1234.567890;
int numPlaces = 5;
String numberSigns = "";
for (int i = 0; i < numPlaces; i++) {
numberSigns += "#";
}
DecimalFormat fmt = new DecimalFormat ("0." + numberSigns);
System.out.println(fmt.format(value));
If you don't need the DecimalFormat for any other purpose, a simpler solution is to use String.format
or PrintStream.format
and generate the format string in a similar manner to Mike Yaworski's solution.如果您不需要 DecimalFormat 用于任何其他目的,一个更简单的解决方案是使用
String.format
或PrintStream.format
并以与 Mike Yaworski 的解决方案类似的方式生成格式字符串。
int precision = 4; // example
String formatString = "%." + precision + "f";
double value = 7.45834975; // example
System.out.format(formatString, value); // output = 7.4583
How about this?这个怎么样?
double value = 10.5555123412341;
int numPlaces = 5;
String format = "0.";
for (int i = 0; i < numPlaces; i++){
format+="#";
}
DecimalFormat fmt = new DecimalFormat(format);
System.out.println(fmt.format(value));
如果您不是绝对必须使用DecimalFormat,
您可以将BigDecimal.round()
与所需精度的MathContext
结合使用,然后只使用BigDecimal.toString().
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