Java How to set Precision for double value

Question

I was working with numbers recently and I had a situation where I want to set the precision of a double value say to 6 digits or 4 digits  depending on the value stored in the database   For example  If in the database the precision is set as 4 digits then the output must look as   10 0000    I tried with DecimalFormat and using the string          but it is annoying to use symbols everytime    Is there any better approach  say something like below   Double value   10 0  value setPrecision 4

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public static String setPrecision String number  int decimal        double nbr   Double valueOf number       int integer Part    int  nbr      double float Part   nbr - integer Part      int floating point    int   Math pow 10  decimal    float Part       String final nbr   String valueOf integer Part          String valueOf floating point       return final nbr

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This is an easy way to do it   String formato   String format    2f      It sets the precision to 2 digits   If you only want to print  use it this way   System out printf    2f  123 234

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BigDecimal value   new BigDecimal 10 0000   value setScale 4

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Here s an efficient way of achieving the result with two caveats    Limits precision to  maximum  N digits  not fixed to N digits   Rounds down the number  not round to nearest     See sample test cases here   123 12345678    gt  123 123 1 230000    gt  1 23 1 1    gt  1 1 1    gt  1 0 0 000    gt  0 0 0 00    gt  0 0 0 4    gt  0 4 0    gt  0 0 1 4999    gt  1 499 1 4995    gt  1 499 1 4994    gt  1 499   Here s the code  The two caveats I mentioned above can be addressed pretty easily  however  speed mattered more to me than accuracy  so i left it here  String manipulations like System out printf    2f  123 234   are computationally costly compared to mathematical operations  In my tests  the below code  without the sysout  took 1 30th the time compared to String manipulations   public double limitPrecision String dblAsString  int maxDigitsAfterDecimal        int multiplier    int  Math pow 10  maxDigitsAfterDecimal       double truncated    double    long    Double parseDouble dblAsString     multiplier     multiplier      System out println dblAsString        gt      truncated       return truncated

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Maybe this method would help you for precising double values   double truncate double number                int integerPart    int  number          double fractionalPart   number - integerPart          fractionalPart    100     It is for upto two decimal values after point                                    You can increase the zeros to fulfill your needs          int fractPart    int  fractionalPart          fractionalPart    double   integerPart     double   fractPart  100          return fractionalPart          This method will allow to set the precision level   double truncate double number  int precision        double prec   Math pow 10  precision       int integerPart    int  number      double fractionalPart   number - integerPart      fractionalPart    prec      int fractPart    int  fractionalPart      fractionalPart    double   integerPart     double   fractPart  prec      return fractionalPart

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You can try BigDecimal for this purpose   Double toBeTruncated   new Double  3 5789055     Double truncatedDouble   BigDecimal valueOf toBeTruncated       setScale 3  RoundingMode HALF UP       doubleValue

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To expand on  EJP  the concept of  precision  when dealing with doubles is extremely fraught  As discussed in https   stackoverflow com a 3730040 390153 you can t even represent 0 1 as a double regardless of the precision  for the same reason you can t represent 1 3 in base 10 with finite precision   You need to consider the problem you are trying to solve  and consider   a  Should I be using doubles in the first place  if precision is a relevant concept  then using doubles may well be a mistake   b  If doubles are appropriate  what do I mean by precision  If you are only talking about display  wrap the logic in a display function and you will only need to deal with it in one place  ie  apply the DRY principle

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To set precision for double values DecimalFormat is good technique  To use this class import java text DecimalFormat and create object of it for example   double no 12 786  DecimalFormat dec   new DecimalFormat   0 00    System out println dec format no      So it will print two digits after decimal point here it will print 12 79

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This worked for me   public static void main String   s            Double d   Math PI          d   Double parseDouble String format    3f   d        can be required precision         System out println d

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The precision of double and float is fixed by their size and the way the IEEE floating point types are implemented   The number of decimal digits in the output  on the other hand  is a matter of formatting  You are correct that typing the same constant over and over is a bad idea  You should declare a string constant instead  and use its symbolic representation   private static final String DBL FMT                Using a symbolic representation would let you change precision in all places the constant is used without searching through your code

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You can t set the precision of a double  or Double  to a specified number of decimal digits  because floating-point values don t have decimal digits  They have binary digits   You will have to convert into a decimal radix  either via BigDecimal or DecimalFormat  depending on what you want to do with the value later   See also my answer to this question for a refutation of the inevitable  100 100 answers

[java] Java: How to set Precision for double value?

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