Using Math round to round to one decimal place

Question

I have these two variables   double num   540 512 double sum   1978 8   Then I did this expression  double total   Math round  num  sum   100    10    10    but I end up with 27 0   In fact I have many other variables and when I use them in the expression I always get a 0 in the tenth s place

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The Math round method returns a long  or an int if you pass in a float   and Java s integer division is the culprit   Cast it back to a double  or use a double literal when dividing by 10   Either   double total    double  Math round  num   sum   100    10    10    or  double total   Math round  num   sum   100    10    10 0    Then you should get  27 3

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A neat alternative that is much more readable in my opinion  however  arguably a tad less efficient due to the conversions between double and String   double num   540 512  double sum   1978 8      NOTE  This does take care of rounding String str   String format    1f    num sum    100 0      If you want the answer as a double  you could of course convert it back   double ans   Double parseDouble str

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Your method is right  all you have to do is add a  0 after both the tens and it will fix your problem   double example   Math round  187 35    10 0    10 0    The output would be   5 3

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DecimalFormat decimalFormat   new DecimalFormat        String result   decimalFormat format 12 763                     -- gt   12 7

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If you need this and similar operations more often  it may be more convenient to find the right library instead of implementing it yourself    Here are one-liners solving your question from Apache Commons Math using Precision  Colt using Functions  and Weka using Utils   double value   540 512   1978 8   100     Apache commons math double rounded1   Precision round value  1   double rounded2   Precision round value  1  BigDecimal ROUND HALF UP      Colt double rounded3   Functions round 0 1  apply value     Weka double rounded4   Utils roundDouble value  1      Maven dependencies     lt dependency gt       lt groupId gt org apache commons lt  groupId gt       lt artifactId gt commons-math3 lt  artifactId gt       lt version gt 3 5 lt  version gt   lt  dependency gt    lt dependency gt       lt groupId gt colt lt  groupId gt       lt artifactId gt colt lt  artifactId gt       lt version gt 1 2 0 lt  version gt   lt  dependency gt    lt dependency gt       lt groupId gt nz ac waikato cms weka lt  groupId gt       lt artifactId gt weka-stable lt  artifactId gt       lt version gt 3 6 12 lt  version gt   lt  dependency gt

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try this  for example  DecimalFormat df   new DecimalFormat          df format 55 544545     output   55 54

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Helpful method I created a while ago     private static double round  double value  int precision        int scale    int  Math pow 10  precision       return  double  Math round value   scale    scale

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Double toBeTruncated   new Double  2 25     Double truncatedDouble   new BigDecimal toBeTruncated  setScale 1  BigDecimal ROUND HALF UP  doubleValue      it will return 2 3

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Double number   new Double  5 25    Double tDouble      new BigDecimal number  setScale 1  BigDecimal ROUND HALF UP  doubleValue      this will return it will return 5 3

[java] Using Math.round to round to one decimal place?

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