user3139293 - 1 year ago 59

Java Question

My code is as follows:

`Number inputAmount = NumberFormat.getNumberInstance(Locale.FRANCE).parse("7,10");`

double doubleValue = inputAmount.doubleValue();

int intValue = (int) (doubleValue * 100);

System.out.println("Input: " + inputAmount);

System.out.println("Double: " + doubleValue);

System.out.println("Integer: " + intValue);

which outputs:

`Input: 7.1`

Double: 7.1

Integer: 710

But, when the

`inputValue`

`Input: 5.1`

Double: 5.1

Integer: 509

This happens only with 5,10 and 4,10. I know that it happens due to the double precision but I cannot figure out exactly how.

Any ideas?

Answer Source

The problem here is, that the multiplication `5.1d * 100d`

produces a rounding error, that results in `509.99999999999994d`

. And when you cast this double into an integer, then the result is obviously `509`

.

To understand what is going on here, consider the following:

```
double doubleValue = 5.1d * 100d; // rounding error...
System.out.println("Double: " + doubleValue);
int intValue = (int) doubleValue;
System.out.println("Integer: " + intValue);
```

Output:

```
Double: 509.99999999999994
Integer: 509
```