Enum Class RoundingMode

java.lang.Object
java.lang.Enum<RoundingMode>
java.math.RoundingMode
All Implemented Interfaces:
Serializable, Comparable<RoundingMode>, Constable 
public enum RoundingMode extends Enum<RoundingMode>
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.

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 Number Result 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, IEEE 754-2019. Where present, this correspondence will be noted in the documentation of the particular constant.
Since:
1.5
See Also:

Nested Class Summary

Nested classes/interfaces declared in class java.lang.Enum

Enum.EnumDesc<E extends Enum<E>>

Enum Constant Summary

Enum Constant Description
CEILING
Rounding mode to round towards positive infinity.
DOWN
Rounding mode to round towards zero.
FLOOR
Rounding mode to round towards negative infinity.
HALF_DOWN
Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round down.
HALF_EVEN
Rounding mode to round towards the "nearest neighbor" unless both neighbors are equidistant, in which case, round towards the even neighbor.
HALF_UP
Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round up.
UNNECESSARY
Rounding mode to assert that the requested operation has an exact result, hence no rounding is necessary.
UP
Rounding mode to round away from zero.

Method Summary

Modifier and Type Method Description
static RoundingMode valueOf(int rm)
Returns the RoundingMode object corresponding to a legacy integer rounding mode constant in BigDecimal.
static RoundingMode valueOf(String name)
Returns the enum constant of this class with the specified name.
static RoundingMode[] values()
Returns an array containing the constants of this enum class, in the order they are declared.

Methods declared in class java.lang.Enum

clone, compareTo, describeConstable, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods declared in class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Details

UP

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

DOWN

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. This mode corresponds to the IEEE 754-2019 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

CEILING

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 754-2019 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

FLOOR

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 754-2019 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_UP

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 754-2019 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

HALF_DOWN

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_EVEN

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. Note that 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 float and double arithmetic in Java. This mode corresponds to the IEEE 754-2019 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

UNNECESSARY

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

Method Details

values

public static RoundingMode[] values()
Returns an array containing the constants of this enum class, in the order they are declared.
Returns:
an array containing the constants of this enum class, in the order they are declared

valueOf

public static RoundingMode valueOf(String name)
Returns the enum constant of this class with the specified name. The string must match exactly an identifier used to declare an enum constant in this class. (Extraneous whitespace characters are not permitted.)
Parameters:
name - the name of the enum constant to be returned.
Returns:
the enum constant with the specified name
Throws:
IllegalArgumentException - if this enum class has no constant with the specified name
NullPointerException - if the argument is null

valueOf

public static RoundingMode valueOf(int rm)
Returns the RoundingMode object corresponding to a legacy integer rounding mode constant in BigDecimal.
Parameters:
rm - legacy integer rounding mode to convert
Returns:
RoundingMode corresponding to the given integer.
Throws:
IllegalArgumentException - integer is out of range

© 1993, 2021, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/math/RoundingMode.html