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java.math

public final Enum RoundingMode

extends Enum<RoundingMode>
Class Inheritance
Annotations
@SuppressWarnings:deprecation
Specifies a rounding policy 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.

More generally, a rounding policy defines a mapping from the real numbers to a subset of representable values. In the case of BigDecimal, the representable values are a function of the precision being used in the computation. Assuming the mathematical result is within the exponent range of BigDecimal, the mathematical result will be exactly representable in the result precision or will fall between two adjacent representable values. In the case of falling between two representable values, the rounding policy determines which of those two bracketing values is the result. For in-range real numbers, for a given set of representable values, a rounding policy maps a continuous segment of the real number line to a single representable value where the real number numerically equal to a representable value is mapped to that value.

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
Input NumberResult of rounding input to one digit with the given rounding mode
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. ).

API Note

Five of the rounding modes declared in this class correspond to rounding-direction attributes defined in the IEEE Standard for Floating-Point Arithmetic. Where present, this correspondence will be noted in the documentation of the particular constant.

Since
1.5
Java Language Specification
15.4 Floating-point Expressions
External Specification
https://standards.ieee.org/ieee/754/6210/
See Also
BigDecimal, MathContext

Field Summary

Modifier and TypeField and Description
public static final RoundingMode
CEILING

Rounding mode to round towards positive infinity.

public static final RoundingMode
DOWN

Rounding mode to round towards zero.

public static final RoundingMode
FLOOR

Rounding mode to round towards negative infinity.

public static final RoundingMode
HALF_DOWN

Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round down.

public static final RoundingMode
HALF_EVEN

Rounding mode to round towards the "nearest neighbor" unless both neighbors are equidistant, in which case, round towards the even neighbor.

public static final RoundingMode
HALF_UP

Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round up.

pack-priv final int
oldMode

public static final RoundingMode
UNNECESSARY

Rounding mode to assert that the requested operation has an exact result, hence no rounding is necessary.

public static final RoundingMode
UP

Rounding mode to round away from zero.

Constructor Summary

AccessConstructor and Description
private
RoundingMode(int
The BigDecimal constant corresponding to this mode
oldMode)

Constructor

Method Summary

Modifier and TypeMethod and Description
public static RoundingMode
valueOf(String name)

public static RoundingMode

Returns:

RoundingMode corresponding to the given integer.
valueOf(int
legacy integer rounding mode to convert
rm)

Returns the RoundingMode object corresponding to a legacy integer rounding mode constant in BigDecimal.

public static RoundingMode[]
values()

Inherited from java.lang.Enum:
clonecompareTodescribeConstableequalsfinalizegetDeclaringClasshashCodenameordinaltoStringvalueOf

Field Detail

CEILINGback to summary
public static final RoundingMode CEILING

Rounding mode to round towards positive infinity. If the result is positive, behaves as for RoundingMode.UP; if negative, behaves as for RoundingMode.DOWN. Note that this rounding mode never decreases the calculated value. This mode corresponds to the IEEE 754 rounding-direction attribute roundTowardPositive.

Example:

Rounding mode CEILING Examples
Input Number Input rounded to one digit
with CEILING rounding
5.5 6
2.5 3
1.6 2
1.1 2
1.0 1
-1.0 -1
-1.1 -1
-1.6 -1
-2.5 -2
-5.5 -5
DOWNback to summary
public static final RoundingMode DOWN

Rounding mode to round towards zero. Never increments the digit prior to a discarded fraction (i.e., truncates). Note that this rounding mode never increases the magnitude of the calculated value.

API Note

This rounding mode is analogous to the rounding policy used for the float and double operators remainder and conversion to an integer value (JLS 15.4). This mode corresponds to the IEEE 754 rounding-direction attribute roundTowardZero.

Example:

Rounding mode DOWN Examples
Input Number Input rounded to one digit
with DOWN rounding
5.5 5
2.5 2
1.6 1
1.1 1
1.0 1
-1.0 -1
-1.1 -1
-1.6 -1
-2.5 -2
-5.5 -5
FLOORback to summary
public static final RoundingMode FLOOR

Rounding mode to round towards negative infinity. If the result is positive, behave as for RoundingMode.DOWN; if negative, behave as for RoundingMode.UP. Note that this rounding mode never increases the calculated value. This mode corresponds to the IEEE 754 rounding-direction attribute roundTowardNegative.

Example:

Rounding mode FLOOR Examples
Input Number Input rounded to one digit
with FLOOR rounding
5.5 5
2.5 2
1.6 1
1.1 1
1.0 1
-1.0 -1
-1.1 -2
-1.6 -2
-2.5 -3
-5.5 -6
HALF_DOWNback to summary
public static final RoundingMode HALF_DOWN

Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round down. Behaves as for RoundingMode.UP if the discarded fraction is > 0.5; otherwise, behaves as for RoundingMode.DOWN.

Example:

Rounding mode HALF_DOWN Examples
Input Number Input rounded to one digit
with HALF_DOWN rounding
5.5 5
2.5 2
1.6 2
1.1 1
1.0 1
-1.0 -1
-1.1 -1
-1.6 -2
-2.5 -2
-5.5 -5
HALF_EVENback to summary
public static final RoundingMode HALF_EVEN

Rounding mode to round towards the "nearest neighbor" unless both neighbors are equidistant, in which case, round towards the even neighbor. Behaves as for RoundingMode.HALF_UP if the digit to the left of the discarded fraction is odd; behaves as for RoundingMode.HALF_DOWN if it's even.

API Note

This is the rounding mode that statistically minimizes cumulative error when applied repeatedly over a sequence of calculations. It is sometimes known as "Banker's rounding," and is chiefly used in the USA. This rounding mode is analogous to the rounding policy used for most float and double arithmetic operators in Java (JLS 15.4). This mode corresponds to the IEEE 754 rounding-direction attribute roundTiesToEven.

Example:

Rounding mode HALF_EVEN Examples
Input Number Input rounded to one digit
with HALF_EVEN rounding
5.5 6
2.5 2
1.6 2
1.1 1
1.0 1
-1.0 -1
-1.1 -1
-1.6 -2
-2.5 -2
-5.5 -6
HALF_UPback to summary
public static final RoundingMode HALF_UP

Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round up. Behaves as for RoundingMode.UP if the discarded fraction is ≥ 0.5; otherwise, behaves as for RoundingMode.DOWN. Note that this is the rounding mode commonly taught at school. This mode corresponds to the IEEE 754 rounding-direction attribute roundTiesToAway.

Example:

Rounding mode HALF_UP Examples
Input Number Input rounded to one digit
with HALF_UP rounding
5.5 6
2.5 3
1.6 2
1.1 1
1.0 1
-1.0 -1
-1.1 -1
-1.6 -2
-2.5 -3
-5.5 -6
oldModeback to summary
pack-priv final int oldMode
UNNECESSARYback to summary
public static final RoundingMode UNNECESSARY

Rounding mode to assert that the requested operation has an exact result, hence no rounding is necessary. If this rounding mode is specified on an operation that yields an inexact result, an ArithmeticException is thrown.

Example:

Rounding mode UNNECESSARY Examples
Input Number Input rounded to one digit
with UNNECESSARY rounding
5.5 throw ArithmeticException
2.5 throw ArithmeticException
1.6 throw ArithmeticException
1.1 throw ArithmeticException
1.0 1
-1.0 -1
-1.1 throw ArithmeticException
-1.6 throw ArithmeticException
-2.5 throw ArithmeticException
-5.5 throw ArithmeticException
UPback to summary
public static final RoundingMode UP

Rounding mode to round away from zero. Always increments the digit prior to a non-zero discarded fraction. Note that this rounding mode never decreases the magnitude of the calculated value.

Example:

Rounding mode UP Examples
Input Number Input rounded to one digit
with UP rounding
5.5 6
2.5 3
1.6 2
1.1 2
1.0 1
-1.0 -1
-1.1 -2
-1.6 -2
-2.5 -3
-5.5 -6

Constructor Detail

RoundingModeback to summary
private RoundingMode(int oldMode)

Constructor

Parameters
oldMode:int

The BigDecimal constant corresponding to this mode

Method Detail

valueOfback to summary
public static RoundingMode valueOf(String name)
valueOfback to summary
public static RoundingMode valueOf(int rm)

Returns the RoundingMode object corresponding to a legacy integer rounding mode constant in BigDecimal.

Parameters
rm:int

legacy integer rounding mode to convert

Returns:RoundingMode

RoundingMode corresponding to the given integer.

Exceptions
IllegalArgumentException:
integer is out of range
valuesback to summary
public static RoundingMode[] values()