12

Here is my function to roundoff a number upto two decimals but when the rounded off number is 1.50 it seems to ignore the trailing zero and just returns 1.5

public static double roundOff(double number) {
        double accuracy = 20;
        number = number * accuracy;
        number = Math.ceil(number);
        number = number / accuracy;
        return number;
    }

So if I send 1.499 it returns 1.5 where as I want 1.50

Nick Div
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    There isn't a separate `double` for 1.5 and for 1.50. They're numerically the same, so there's only one `double` representation of them both. – Dawood ibn Kareem Jan 08 '15 at 02:48
  • Maybe your method should return `String`, rather than `double`, so that you can do whatever kind of formatting you want with it. – Dawood ibn Kareem Jan 08 '15 at 02:50
  • Are you sure about that `20`? Maybe I misunderstood what you are trying to do, but your method for `1.489` wouldn't return `1.49`. I would think you'd want to set accuracy to `100` for two decimal places. – cyon Jan 08 '15 at 02:59
  • @cyon, it should round it up to the next multiple of 1/20, so 1.499 will indeed become 1.5. But you're right that it doesn't gel with the "up to two decimals" comment. – paxdiablo Jan 08 '15 at 03:06

4 Answers4

24

This is a printing poblem:

double d = 1.5;
System.out.println(String.format("%.2f", d)); // 1.50
Jean Logeart
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4

1.5 is, number of significant digits notwithstanding, the same as 1.50 (and even 1.5000000000000).

You need to separate the value of the number from its presentation.

If you want it output with two decimal digits, just use String.format, such as with:

public class Test
{
    public static void main(String[] args) {
        double d = 1.50000;
        System.out.println(d);
        System.out.println(String.format("%.2f", d));
    }
}

which outputs:

1.5
1.50

If you still want a function that does all that for you and gives you a specific format, you'll need to return the string with something like:

public static String roundOff(double num, double acc, String fmt) {
    num *= acc;
    num = Math.ceil(num);
    num /= acc;
    return String.format(fmt, num);
}

and call it with:

resultString = roundOff(value, 20, "%.2f"); // or 100, see below.

This will allow you to tailor the accuracy and output format in any way you desire, although you can still hard-code the values if you want simplicity:

public static String roundOff(double num) {
    double acc = 20;
    String fmt = "%.2f";
    num *= acc;
    num = Math.ceil(num);
    num /= acc;
    return String.format(fmt, num);
}

One final note: your question states that you want to round to "two decimals" but that doesn't quite gel with your use of 20 as the accuracy, since that will round it up to the next multiple of 1/20. If you really want it rounded up to two decimals, the value you should be using for accuracy is 100.

Dawood ibn Kareem
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paxdiablo
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  • In your last little snippet, you have two different variables called `acc` (one parameter, one local) and two different variables called `fmt`. Then you use a variable called `accuracy` which appears not to exist. You might want to fix this. – Dawood ibn Kareem Jan 08 '15 at 03:23
  • @David, _damn_ those cut'n'paste errors :-) Thanks for that, fixed now. – paxdiablo Jan 08 '15 at 04:58
  • Sorry, I really should have just edited it myself. It was clear from the words that you meant those two variables to be locals, not parameters. – Dawood ibn Kareem Jan 08 '15 at 05:00
2

You will have to format it as a String in order to do that. Java, like most languages, will drop the trailing zero. 

String.format("%.2f", number);

So you can either return a String (change your return type from double) or just format it when you need to display it using the code above. You can read the JavaDoc for Formatter in order to understand all of the possibilities with number of decimal places, comma placement, etc.

Todd
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  • Thanks, Jean's solution which is the same as your's worked smoothly. – Nick Div Jan 08 '15 at 02:54
  • Just one note, though it doesn't affect the output: the `1` in your format string has little effect here since it sets the minimum field width for the whole thing. Since you're also specifying it be of the form `.99`, it already has to be more than that. – paxdiablo Jan 08 '15 at 02:56
  • Thanks @paxdiablo. I had it as something different (formatted with comma separator which I use personally) and then changed it to be simpler and in my haste left the "1." in. Corrected now, thank you! – Todd Jan 08 '15 at 02:57
1

You can try this if you want is a String output

double number = roundOff(1.499);//1.5

DecimalFormat decimalFormat = new DecimalFormat("#.00");
String fromattedDouble = decimalFormat.format(number);//1.50

The function roundOff is the same as you mentioned in your question.

Sreekanth
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