10

The following code:

double doubleValue = 1713.6;
float floatValue = 1713.6f;
String fs = "%-9s : %-7s %-7s\n";
System.out.printf( fs, "", "double", "float" );

DecimalFormat format = new DecimalFormat("#0");
System.out.printf( fs, "toString", String.valueOf( doubleValue ), String.valueOf( floatValue ) );

format.setRoundingMode( RoundingMode.DOWN );
System.out.printf( fs, "DOWN", format.format( doubleValue ), format.format( floatValue ) );

format.setRoundingMode( RoundingMode.HALF_DOWN );
System.out.printf( fs, "HALF_DOWN", format.format( doubleValue ), format.format( floatValue ) );

format.setRoundingMode( RoundingMode.HALF_UP );
System.out.printf( fs, "HALF_UP", format.format( doubleValue ), format.format( floatValue ) );

format.setRoundingMode( RoundingMode.UP );
System.out.printf( fs, "UP", format.format( doubleValue ), format.format( floatValue ) );

Produces the result (live code):

          : double  float  
toString  : 1713.6  1713.6 
DOWN      : 1713    1713   
HALF_DOWN : 1714    1714   
HALF_UP   : 1713    1714   <--- notice this line
UP        : 1714    1714

I know that certain numbers cannot be represented exactly as floating-point numbers. The actual floating-point representation for 1713.6 is 1713.5999755859375 (see this page).

But why does HALF_UP round down in this case?

Using Java 1.8u25

GreenGiant
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2 Answers2

14

There was a bug in Java 8 regarding the NumberFormat and RoundingMod HALF_UP see 8039915. This was fixed with 8u40 (Release Notes).

turbanoff
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mszalbach
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1

Ideone is using sun-jdk-8u25 where this buggy behavior is appearing.

On Java 1.7, I'm getting HALF_UP : 1714 1714 which is right.

enum RoundingMode - Specifies a rounding behavior for numerical operations capable of discarding precision.

See Oracle javadoc: Result of rounding input to one digit with the given rounding mode[Rounding Mode Table]

Rajesh
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