How to round 0 745 to 0 75 using BigDecimal ROUND HALF UP

Question

I tried the following      double doubleVal   1 745     double doubleVal1   0 745     BigDecimal bdTest   new BigDecimal   doubleVal      BigDecimal bdTest1   new BigDecimal   doubleVal1       bdTest   bdTest setScale 2  BigDecimal ROUND HALF UP      bdTest1   bdTest1 setScale 2  BigDecimal ROUND HALF UP      System out println  bdTest   bdTest     1 75    System out println  bdTest1   bdTest1    0 74    problemmmm                  but got weird results  Why

User · Accepted Answer

Never construct BigDecimals from floats or doubles. Construct them from ints or strings. floats and doubles loose precision.

This code works as expected (I just changed the type from double to String):

public static void main(String[] args) {
  String doubleVal = "1.745";
  String doubleVal1 = "0.745";
  BigDecimal bdTest = new BigDecimal(  doubleVal);
  BigDecimal bdTest1 = new BigDecimal(  doubleVal1 );
  bdTest = bdTest.setScale(2, BigDecimal.ROUND_HALF_UP);
  bdTest1 = bdTest1.setScale(2, BigDecimal.ROUND_HALF_UP);
  System.out.println("bdTest:"+bdTest); //1.75
  System.out.println("bdTest1:"+bdTest1);//0.75, no problem
}

User · Answer

This will maybe give you a hint on what went wrong   import java math BigDecimal   public class Main       public static void main String   args            BigDecimal bdTest   new BigDecimal 0 745           BigDecimal bdTest1   new BigDecimal  0 745            bdTest   bdTest setScale 2  BigDecimal ROUND HALF UP           bdTest1   bdTest1 setScale 2  BigDecimal ROUND HALF UP           System out println  bdTest     bdTest      prints  bdTest 0 74          System out println  bdTest1     bdTest1      prints  bdTest 0 75            The problem is  that your input  a double x 0 745   can not represent 0 745 exactly  It actually saves a value slightly lower  For BigDecimals  this is already below 0 745  so it rounds down     Try not to use the BigDecimal double float  constructors

User · Answer

double doubleVal   1 745  double doubleVal1   0 745  System out println new BigDecimal doubleVal    System out println new BigDecimal doubleVal1      outputs   1 74500000000000010658141036401502788066864013671875 0 74499999999999999555910790149937383830547332763671875   Which shows the real value of the two doubles and explains the result you get  As pointed out by others  don t use the double constructor  apart from the specific case where you want to see the actual value of a double    More about double precision    here there

User · Answer

various option are available such as   Double d  123 12  BigDecimal b   new BigDecimal d  MathContext DECIMAL64      b   123 1200000 b   b setScale 2  BigDecimal ROUND HALF UP       b   123 12  BigDecimal b1  new BigDecimal collectionFileData getAmount    MathContext DECIMAL64  setScale 2  BigDecimal ROUND HALF UP      b1  123 12   d    double  Math round d   100    100  BigDecimal b2   new BigDecimal d toString         b2  123 12

User · Answer

Use BigDecimal valueOf double d  instead of new BigDecimal double d   The last one has precision errors by float and double

User · Answer

For your interest  to do the same with double  double doubleVal   1 745  double doubleVal2   0 745  doubleVal   Math round doubleVal   100   0 005    100 0  doubleVal2   Math round doubleVal2   100   0 005    100 0  System out println  bdTest      doubleVal     1 75 System out println  bdTest1      doubleVal2    0 75   or just  double doubleVal   1 745  double doubleVal2   0 745  System out printf  bdTest    2f n    doubleVal   System out printf  bdTest1    2f n    doubleVal2     both print  bdTest  1 75 bdTest1  0 75   I prefer to keep code as simple as possible      As  mshutov notes  you need to add a little more to ensure that a half value always rounds up  This is because numbers like 265 335 are a little less than they appear

[java] How to round 0.745 to 0.75 using BigDecimal.ROUND_HALF_UP?

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