How accurate is BigDecimal.doubleValue() if no operation is applied on the amount

Question

I NEED to be sending a value as 'double', however I am:

1. Taking a value as a long
2. Converting it to BigDecimal
3. Calling method scaleByPowerOfTen on the BigDecimal (using '-2' to make cents a whole amount value).
4. Calling doubleValue() on the BigDecimal to get the needed value as double.

Now I know that double values lose precision when you apply arithmetic operations on them, however what could I possibly get if I try to send a double value as-is based on BigDecimal, such as (I believe) the above scenario is.

This is important as I have to be sending money values over SOAP in this manner - no other way.

I also have the scenario where the BigDecimal is created using as a String, then doubleValue() is called on it. What could I get in this case ?

EDIT: Sample code for this:

long amountInCents = 1852;
BigDecimal amountInWholeUnits = BigDecimal.valueOf(amountInCents).scaleByPowerOfTen(-2);
double amountToSend = amountInWholeUnits.doubleValue();

As for the case where the amount is provided as String:

double amountToSend = new BigDecimal("18.52").doubleValue();

UPDATE

Now that I have sample code, I just thought I can test and see, so I did a for loop and used System.out.println: so far so good, the values are correct, so I believe this will be the same when sent through SOAP. Please correct me if I'm wrong.

Answer 1

Since one cent is equal to 1/100 of a dollar, and since the number 1/100 or 0.01 cannot be represented exactly as a binary floating-point number, some slight loss of accuracy will occur. In your particular example of $18.52, the resulting double will hold the closest double value to 18.52, but it will not be exactly equal to 18.52.