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

User · Answer

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:

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-math3</artifactId>
    <version>3.5</version>
</dependency>

<dependency>
    <groupId>colt</groupId>
    <artifactId>colt</artifactId>
    <version>1.2.0</version>
</dependency>

<dependency>
    <groupId>nz.ac.waikato.cms.weka</groupId>
    <artifactId>weka-stable</artifactId>
    <version>3.6.12</version>
</dependency>

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

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

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