java - ArithmeticException: "Non-terminating decimal expansion; no exact representable decimal result"

Question

Why does the following code raise the exception shown below?

BigDecimal a = new BigDecimal("1.6");
BigDecimal b = new BigDecimal("9.2");
a.divide(b) // results in the following exception.

Exception:

java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result.

Answer 1

From the Java 11 BigDecimal docs:

When a MathContext object is supplied with a precision setting of 0 (for example, MathContext.UNLIMITED), arithmetic operations are exact, as are the arithmetic methods which take no MathContext object. (This is the only behavior that was supported in releases prior to 5.)

As a corollary of computing the exact result, the rounding mode setting of a MathContext object with a precision setting of 0 is not used and thus irrelevant. In the case of divide, the exact quotient could have an infinitely long decimal expansion; for example, 1 divided by 3.

If the quotient has a nonterminating decimal expansion and the operation is specified to return an exact result, an ArithmeticException is thrown. Otherwise, the exact result of the division is returned, as done for other operations.

To fix, you need to do something like this:

a.divide(b, 2, RoundingMode.HALF_UP)

where 2 is the scale and RoundingMode.HALF_UP is rounding mode

For more details see this blog post.