What s the best practice to round a float to 2 decimals

Question

I m using eclipse   Android SDK   I need to round a float value to 2 decimals  I usually use the next  trick  using Math library   float accelerometerX   accelerometerX   100      accelerometerX   round accelerometerX       Log d  Test       accelerometerX 100     But I feel it is not the best way to do it   Is there a library to do these type of operations

User · Answer

by importing Decimal format we can do     import java util Scanner  import java text DecimalFormat  public class Average   public static void main String   args    int sub1 sub2 sub3 total  Scanner in   new Scanner System in   System out print  Enter Subject 1 Marks       sub1   in nextInt    System out print  Enter Subject 2 Marks       sub2   in nextInt    System out print  Enter Subject 3 Marks       sub3   in nextInt    total   sub1   sub2   sub3  System out println  Total Marks of Subjects       total   res    float total  average   res 3  System out println  Before Rounding Decimal   Average      average        DecimalFormat df   new DecimalFormat            System out println  After Rounding Decimal   Average      df format average               Output Enter Subject 1 Marks   72 Enter Subject 2 Marks   42 Enter Subject 3 Marks   52 Total Marks of Subjects   166 Before Rounding Decimal   Average   55 333332  After Rounding Decimal   Average   55 33         Output Enter Subject 1 Marks   98 Enter Subject 2 Marks   88 Enter Subject 3 Marks   78 Total Marks of Subjects   264 Before Rounding Decimal   Average   88 0  After Rounding Decimal   Average   88         You can Find Avrerage values in two ouputs before rounding average And After rounding Average

User · Answer

I was working with statistics in Java 2 years ago and I still got the codes of a function that allows you to round a number to the number of decimals that you want  Now you need two  but maybe you would like to try with 3 to compare results  and this function gives you this freedom           Round to certain number of decimals       param d    param decimalPlace    return    public static float round float d  int decimalPlace        BigDecimal bd   new BigDecimal Float toString d        bd   bd setScale decimalPlace  BigDecimal ROUND HALF UP       return bd floatValue        You need to decide if you want to round up or down  In my sample code I am rounding up   Hope it helps   EDIT  If you want to preserve the number of decimals when they are zero  I guess it is just for displaying to the user  you just have to change the function type from float to BigDecimal  like this   public static BigDecimal round float d  int decimalPlace        BigDecimal bd   new BigDecimal Float toString d        bd   bd setScale decimalPlace  BigDecimal ROUND HALF UP              return bd      And then call the function this way   float x   2 3f  BigDecimal result  result round x 2   System out println result     This will print   2 30

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I ve tried to support the -ve values for  Ivan Stin  excellent 2nd method   Major credit goes to  Ivan Stin for his method   public static float round float value  int scale        int pow   10      for  int i   1  i  lt  scale  i              pow    10            float tmp   value   pow      float tmpSub   tmp -  int  tmp       return    float     int                value  gt   0                tmpSub  gt   0 5f   tmp   1   tmp                 tmpSub  gt   -0 5f   tmp   tmp - 1                      pow          Below will only handles  ve values        return    float     int    tmp -  int  tmp   gt   0 5f   tmp   1   tmp        pow      Below are the tests cases I ve tried  Please let me know if this is not addressing any other cases    Test public void testFloatRound             ve values     Assert assertEquals 0F  NumberUtils round 0F   0       Assert assertEquals 1F  NumberUtils round 1F   0       Assert assertEquals 23 46F  NumberUtils round 23 4567F   0       Assert assertEquals 23 45F  NumberUtils round 23 4547F   0D       Assert assertEquals 1 00F  NumberUtils round 0 49999999999999994F   0 5F   0       Assert assertEquals 123 12F  NumberUtils round 123 123F   0       Assert assertEquals 0 12F  NumberUtils round 0 123F   0       Assert assertEquals 0 55F  NumberUtils round 0 55F   0       Assert assertEquals 0 55F  NumberUtils round 0 554F   0       Assert assertEquals 0 56F  NumberUtils round 0 556F   0       Assert assertEquals 123 13F  NumberUtils round 123 126F   0       Assert assertEquals 123 15F  NumberUtils round 123 15F   0       Assert assertEquals 123 17F  NumberUtils round 123 1666F   0       Assert assertEquals 123 46F  NumberUtils round 123 4567F   0       Assert assertEquals 123 87F  NumberUtils round 123 8711F   0       Assert assertEquals 123 15F  NumberUtils round 123 15123F   0       Assert assertEquals 123 89F  NumberUtils round 123 8909F   0       Assert assertEquals 124 00F  NumberUtils round 123 9999F   0       Assert assertEquals 123 70F  NumberUtils round 123 7F   0       Assert assertEquals 123 56F  NumberUtils round 123 555F   0       Assert assertEquals 123 00F  NumberUtils round 123 00F   0       Assert assertEquals 123 50F  NumberUtils round 123 50F   0       Assert assertEquals 123 93F  NumberUtils round 123 93F   0       Assert assertEquals 123 93F  NumberUtils round 123 9312F   0       Assert assertEquals 123 94F  NumberUtils round 123 9351F   0       Assert assertEquals 123 94F  NumberUtils round 123 9350F   0       Assert assertEquals 123 94F  NumberUtils round 123 93501F   0       Assert assertEquals 99 99F  NumberUtils round 99 99F   0       Assert assertEquals 100 00F  NumberUtils round 99 999F   0       Assert assertEquals 100 00F  NumberUtils round 99 9999F   0           -ve values     Assert assertEquals -123 94F  NumberUtils round -123 93501F   0       Assert assertEquals -123 00F  NumberUtils round -123 001F   0       Assert assertEquals -0 94F  NumberUtils round -0 93501F   0       Assert assertEquals -1F  NumberUtils round -1F   0       Assert assertEquals -0 50F  NumberUtils round -0 50F   0       Assert assertEquals -0 55F  NumberUtils round -0 55F   0       Assert assertEquals -0 55F  NumberUtils round -0 554F   0       Assert assertEquals -0 56F  NumberUtils round -0 556F   0       Assert assertEquals -0 12F  NumberUtils round -0 1234F   0       Assert assertEquals -0 12F  NumberUtils round -0 123456789F   0       Assert assertEquals -0 13F  NumberUtils round -0 129F   0       Assert assertEquals -99 99F  NumberUtils round -99 99F   0       Assert assertEquals -100 00F  NumberUtils round -99 999F   0       Assert assertEquals -100 00F  NumberUtils round -99 9999F   0

User · Answer

double roundTwoDecimals double d      DecimalFormat twoDForm   new DecimalFormat            return Double valueOf twoDForm format d

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Here is a simple one-line solution    int    value   0 005f    100     100f

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Here is a shorter implementation comparing to  Jav Rock s                Round to certain number of decimals                 param d         param decimalPlace the numbers of decimals         return              public static float round float d  int decimalPlace             return BigDecimal valueOf d  setScale decimalPlace BigDecimal ROUND HALF UP  floatValue                 System out println round 2 345f 2     two decimal digits    2 35

User · Answer

Let s test 3 methods  1   public static double round1 double value  int scale        return Math round value   Math pow 10  scale     Math pow 10  scale       2    public static float round2 float number  int scale        int pow   10      for  int i   1  i  lt  scale  i            pow    10      float tmp   number   pow      return    float     int    tmp -  int  tmp   gt   0 5f   tmp   1   tmp        pow      3   public static float round3 float d  int decimalPlace        return BigDecimal valueOf d  setScale decimalPlace  BigDecimal ROUND HALF UP  floatValue         Number is 0 23453f We ll test 100 000 iterations each method   Results  Time 1 - 18 ms Time 2 - 1 ms Time 3 - 378 ms  Tested on laptop Intel i3-3310M CPU 2 4GHz

[java] What's the best practice to round a float to 2 decimals?

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