RoundingMode (Java SE 26 & JDK 26)
Description: declaration: module: java.base, package: java.math, enum: RoundingMode
Keywords: java.math.RoundingMode class

# 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.

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 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. Where present, this correspondence will be noted in the documentation of the particular constant.
See Java Language Specification:
  15.4 Floating-point Expressions
Since:
  1.5
External Specifications
  - IEEE Standard for Floating-Point Arithmetic
See Also:
  - `BigDecimal`
  - `MathContext`

- ## Nested Class Summary

  ### Nested classes/interfaces declared in class Enum

  `Enum.EnumDesc<E>`
  Modifier and Type
  Class
  Description
  `static final class`
  `Enum.EnumDesc<E extends Enum<E>>`
  A nominal descriptor for an `enum` constant.

- ## Enum Constant Summary

  Enum Constants
  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 Enum

  `clone, compareTo, describeConstable, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf`
  Modifier and Type
  Method
  Description
  `protected final Object`
  `clone()`
  Throws CloneNotSupportedException.
  `final int`
  `compareTo(RoundingMode o)`
  Compares this enum with the specified object for order.
  `final Optional<Enum.EnumDesc<RoundingMode>>`
  `describeConstable()`
  Returns an enum descriptor `EnumDesc` for this instance, if one can be constructed, or an empty `Optional` if one cannot be.
  `final boolean`
  `equals(Object other)`
  Returns true if the specified object is equal to this enum constant.
  `protected final void`
  `finalize()`
  Deprecated, for removal: This API element is subject to removal in a future version.
  Finalization has been deprecated for removal.
  `final Class<RoundingMode>`
  `getDeclaringClass()`
  Returns the Class object corresponding to this enum constant's enum type.
  `final int`
  `hashCode()`
  Returns a hash code for this enum constant.
  `final String`
  `name()`
  Returns the name of this enum constant, exactly as declared in its enum declaration.
  `final int`
  `ordinal()`
  Returns the ordinal of this enumeration constant (its position in its enum declaration, where the initial constant is assigned an ordinal of zero).
  `String`
  `toString()`
  Returns the name of this enum constant, as contained in the declaration.
  `static <T extends Enum<T>>
  T`
  `valueOf(Class<T> enumClass, String name)`
  Returns the enum constant of the specified enum class with the specified name.

  ### Methods declared in class Object

  `getClass, notify, notifyAll, wait, wait, wait`
  Modifier and Type
  Method
  Description
  `final Class<?>`
  `getClass()`
  Returns the runtime class of this `Object`.
  `final void`
  `notify()`
  Wakes up a single thread that is waiting on this object's monitor.
  `final void`
  `notifyAll()`
  Wakes up all threads that are waiting on this object's monitor.
  `final void`
  `wait()`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
  `final void`
  `wait(long timeoutMillis)`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
  `final void`
  `wait(long timeoutMillis, int nanos)`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

- ## 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.
    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

  - ### 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 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 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 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.
    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

  - ### 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