Specifies a
rounding behavior for numerical operations
capable of discarding precision. Each rounding mode indicates how
the least significant returned digit of a rounded result is to be
calculated. If fewer digits are returned than the digits needed to
represent the exact numerical result, the discarded digits will be
referred to as the
discarded fraction regardless the digits'
contribution to the value of the number. In other words,
considered as a numerical value, the discarded fraction could have
an absolute value greater than one.
Each rounding mode description includes a table listing how
different two-digit decimal values would round to a one digit
decimal value under the rounding mode in question. The result
column in the tables could be gotten by creating a
BigDecimal number with the specified value, forming a
MathContext
object with the proper settings
(precision set to 1, and the
roundingMode set to the rounding mode in question), and
calling round
on this number with the
proper MathContext. A summary table showing the results
of these rounding operations for all rounding modes appears below.
Summary of Rounding Operations Under Different Rounding Modes
| Result of rounding input to one digit with the given
rounding mode |
---|
Input Number | UP |
DOWN |
CEILING |
FLOOR |
HALF_UP |
HALF_DOWN |
HALF_EVEN |
UNNECESSARY |
5.5 | 6 | 5 | 6 | 5 | 6 | 5 | 6 | throw ArithmeticException |
2.5 | 3 | 2 | 3 | 2 | 3 | 2 | 2 | throw ArithmeticException |
1.6 | 2 | 1 | 2 | 1 | 2 | 2 | 2 | throw ArithmeticException |
1.1 | 2 | 1 | 2 | 1 | 1 | 1 | 1 | throw ArithmeticException |
1.0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
-1.0 | -1 | -1 | -1 | -1 | -1 | -1 | -1 | -1 |
-1.1 | -2 | -1 | -1 | -2 | -1 | -1 | -1 | throw ArithmeticException |
-1.6 | -2 | -1 | -1 | -2 | -2 | -2 | -2 | throw ArithmeticException |
-2.5 | -3 | -2 | -2 | -3 | -3 | -2 | -2 | throw ArithmeticException |
-5.5 | -6 | -5 | -5 | -6 | -6 | -5 | -6 | throw ArithmeticException |
This enum is intended to replace the integer-based
enumeration of rounding mode constants in BigDecimal
(BigDecimal.ROUND_UP
, BigDecimal.ROUND_DOWN
,
etc. ).