Long to String before converting to a BigDecimal

Question

I have to convert a Long (Object one, contained in the variable 'longValueToConvert') to a BigDecimal.

I would have done something like this :

new BigDecimal(longValueToConvert)

But i've read that this cast could induce errors in the conversion and that it is prefered to cast the Long to a String before using it to the BigDecimal constructor.

new BigDecimal(longValueToConvert.toString())

Is it Ok to use the first one or the second one would be preferable ? I use Java 8.

Answer 1

You heard wrong. There is no conversion error from the BigDecimal(long) constructor. A long can be represented exactly and there is no problem making a BigDecimal out of it.

You need to be careful only when you use the BigDecimal(double) constructor. This is because some double values can't be represented exactly. From the documentation:

The results of this constructor can be somewhat unpredictable. One might assume that writing new BigDecimal(0.1) in Java creates a BigDecimal which is exactly equal to 0.1 [...], but it is actually equal to 0.1000000000000000055511151231257827021181583404541015625. This is because 0.1 cannot be represented exactly as a double [...].

The String constructor, on the other hand, is perfectly predictable: writing new BigDecimal("0.1") creates a BigDecimal which is exactly equal to 0.1, as one would expect. Therefore, it is generally recommended that the String constructor be used in preference to this one.