Question

basic java question. rounding decimal.

Answer 1

alright so I have a program that is supposed to calculate the surface area of a cylinder. The exact answer to it for radius 2 and height 5 is \(28 \pi\). I want it to show \(28 \pi \text { not } 28.0\pi\) the problem I am having is sometimes it would have to show like \(24.5\pi\) and other times it might be a repeating decimal like \(24.3333333...\pi\). Is there a way to make it round only when appropriate?

Answer 2

because I know I can do Math.round, but that would mess up the 24.5 one. I want it to display no decimal place if it is exactly an integer number, and not to round if is not an integer number.

Answer 3

Hey,
So I'm not quite sure what you'd want to display in the case of 2.33...pi: is it 2.33pi or 2.33....pi? Because the latter might be a bit tricker :)

But for the other examples you might want to take a look at the DecimalFormat class.
API link: http://docs.oracle.com/javase/1.4.2/docs/api/java/text/DecimalFormat.html

Let me know if that works for you,
Best,

Answer 4

public class RoundTwoDecimalPlaces{
public static void main(String[] args) {
float num = 2.954165f;
float round = Round(num,2);
System.out.println("Rounded data: " + round);
}

public static float Round(float Rval, int Rpl) {
float p = (float)Math.pow(10,Rpl);
Rval = Rval * p;
float tmp = Math.round(Rval);
return (float)tmp/p;
}
}

Answer 5

Just for a different point of view, do you want the math value changed or is this a print formatting issue?