Java，将小数点后两位取整

Question

I'm trying to round a double to the nearest two decimal places however, it is just rounding to the nearest full number.

For example, 19634.0 instead of 19634.95.

This is the current code I use for the rounding

double area = Math.round(Math.PI*Radius()*Radius()*100)/100;

I can't see where i am going wrong.

Many thanks for any help.

Answer 1

Well, Math.round(Math.PI*Radius()*Radius()*100) is long . 100 is int .

So Math.round(Math.PI*Radius()*Radius()*100) / 100 will become long ( 19634 ).

Change it to Math.round(Math.PI*Radius()*Radius()*100) / 100.0 . 100.0 is double , and the result will also be double ( 19634.95 ).

Answer 2

Do you actually want want to round the value to 2 places, which will cause snowballing rounding errors in your code, or simply display the number with 2 decimal places? Check out String.format() . Complex but very powerful.

Answer 3

You can use a DecimalFormat object:

DecimalFormat df = new DecimalFormat ();
df.setMaximumFractionDigits (2);
df.setMinimumFractionDigits (2);

System.out.println (df.format (19634.95));

Answer 4

You might want to take a look at the DecimalFormat class.

double x = 4.654;

DecimalFormat twoDigitFormat = new DecimalFormat("#.00");
System.out.println("x=" + twoDigitFormat.format());

This gives "x=4.65". The difference between # and 0 in the pattern is that the zeros are always displayed and # will not if the last ones are 0.

Answer 5

The following example came from this forum , but seems to be what you are looking for.

 double roundTwoDecimals(double d) {
      DecimalFormat twoDForm = new DecimalFormat("#.##");
      return Double.valueOf(twoDForm.format(d));
 }