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 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.
See Java Language Specification:
15.4 Floating-point Expressions
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 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 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.
      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