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Thread: How to make Math.round() round to the nearest .1?

  1. #1
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    Default How to make Math.round() round to the nearest .1?

    I want round to round to the nearest 10th instead of the nearest integer... Any ideas?

    public class Triangle 
    {
        private final int leg;
        private final double hypotenuse;
     
        public Triangle( int l )
        {
            leg = l;
            hypotenuse = leg*Math.sqrt( 2.0 );
        }    
     
        public int getLeg()
        {
            return leg;
        }
     
        public double getHypotenuse()
        {
            return hypotenuse;
        }
     
        @Override
        public String toString()
        {
            return String.format( "Triangle(%d)", leg );
        }
    }

    Triangle(5)
    Leg: 5
    Hypotenuse: 7.0 (this should be 7.1)


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: How to make Math.round() round to the nearest .1?

    One idea: *10, round, /10
    If you don't understand my answer, don't ignore it, ask a question.

  3. The Following User Says Thank You to Norm For This Useful Post:

    bdennin (February 2nd, 2013)

  4. #3
    Super Moderator pbrockway2's Avatar
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    Default Re: How to make Math.round() round to the nearest .1?

    Do do you want to round the value hypotenuse - ie produce a completely different double value - or merely format the value so that it appears with one decimal place?

    I ask because people often confuse rounding (double->double) with formatting (double->String). And often imagine that double values have decimal places: in fact decimal places are a property of the String (base 10) representation of double values.

    Assuming you want to format you would use

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

    The "f" means you are formatting a floating point value (a double) and the ".1" means you want one decimal place to appear.

    Full details in the Formatter API docs. There is rather a lot to absorb there: too much to attempt to remember. But it's worth bookmarking and going back to whenever formatting problems arise.

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    bdennin (February 2nd, 2013)

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    Default Re: How to make Math.round() round to the nearest .1?

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

    Ahhh, so easy. I can't believe I didn't think of that. Thank you, as always.

  7. #5
    Super Moderator pbrockway2's Avatar
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    Default Re: How to make Math.round() round to the nearest .1?

    You're welcome.

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