/* * Copyright (c) 2003, 2011, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. * * * * * * * * * * * * * * * * * * * * */ /* * Portions Copyright IBM Corporation, 2001. All Rights Reserved. */ package java.math; /** * 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 * {@code BigDecimal} number with the specified value, forming a * {@link MathContext} object with the proper settings * ({@code precision} set to {@code 1}, and the * {@code roundingMode} set to the rounding mode in question), and * calling {@link BigDecimal#round round} on this number with the * proper {@code 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 {@code UP}{@code DOWN}{@code CEILING}{@code FLOOR}{@code HALF_UP}{@code HALF_DOWN}{@code HALF_EVEN}{@code UNNECESSARY}
5.5 6 5 6 5 6 5 6 throw {@code ArithmeticException}
2.5 3 2 3 2 3 2 2 throw {@code ArithmeticException}
1.6 2 1 2 1 2 2 2 throw {@code ArithmeticException}
1.1 2 1 2 1 1 1 1 throw {@code 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 {@code ArithmeticException}
-1.6 -2 -1 -1 -2 -2 -2 -2 throw {@code ArithmeticException}
-2.5 -3 -2 -2 -3 -3 -2 -2 throw {@code ArithmeticException}
-5.5 -6 -5 -5 -6 -6 -5 -6 throw {@code ArithmeticException}
* * *

This {@code enum} is intended to replace the integer-based * enumeration of rounding mode constants in {@link BigDecimal} * ({@link BigDecimal#ROUND_UP}, {@link BigDecimal#ROUND_DOWN}, * etc. ). * * @see BigDecimal * @see MathContext * @author Josh Bloch * @author Mike Cowlishaw * @author Joseph D. Darcy * @since 1.5 */ public enum RoundingMode { /** * 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: * * * * * * * * * * * * *
Input NumberInput rounded to one digit
with {@code 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
*/ UP(BigDecimal.ROUND_UP), /** * 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. * *

Example: * * * * * * * * * * * * *
Input NumberInput rounded to one digit
with {@code 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
*/ DOWN(BigDecimal.ROUND_DOWN), /** * Rounding mode to round towards positive infinity. If the * result is positive, behaves as for {@code RoundingMode.UP}; * if negative, behaves as for {@code RoundingMode.DOWN}. Note * that this rounding mode never decreases the calculated value. * *

Example: * * * * * * * * * * * * *
Input NumberInput rounded to one digit
with {@code 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
*/ CEILING(BigDecimal.ROUND_CEILING), /** * Rounding mode to round towards negative infinity. If the * result is positive, behave as for {@code RoundingMode.DOWN}; * if negative, behave as for {@code RoundingMode.UP}. Note that * this rounding mode never increases the calculated value. * *

Example: * * * * * * * * * * * * *
Input NumberInput rounded to one digit
with {@code 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
*/ FLOOR(BigDecimal.ROUND_FLOOR), /** * Rounding mode to round towards {@literal "nearest neighbor"} * unless both neighbors are equidistant, in which case round up. * Behaves as for {@code RoundingMode.UP} if the discarded * fraction is ≥ 0.5; otherwise, behaves as for * {@code RoundingMode.DOWN}. Note that this is the rounding * mode commonly taught at school. * *

Example: * * * * * * * * * * * * *
Input NumberInput rounded to one digit
with {@code 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_UP(BigDecimal.ROUND_HALF_UP), /** * Rounding mode to round towards {@literal "nearest neighbor"} * unless both neighbors are equidistant, in which case round * down. Behaves as for {@code RoundingMode.UP} if the discarded * fraction is > 0.5; otherwise, behaves as for * {@code RoundingMode.DOWN}. * *

Example: * * * * * * * * * * * * *
Input NumberInput rounded to one digit
with {@code 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_DOWN(BigDecimal.ROUND_HALF_DOWN), /** * Rounding mode to round towards the {@literal "nearest neighbor"} * unless both neighbors are equidistant, in which case, round * towards the even neighbor. Behaves as for * {@code RoundingMode.HALF_UP} if the digit to the left of the * discarded fraction is odd; behaves as for * {@code 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 {@literal "Banker's rounding,"} and is * chiefly used in the USA. This rounding mode is analogous to * the rounding policy used for {@code float} and {@code double} * arithmetic in Java. * *

Example: * * * * * * * * * * * * *
Input NumberInput rounded to one digit
with {@code 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_EVEN(BigDecimal.ROUND_HALF_EVEN), /** * 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 * {@code ArithmeticException} is thrown. *

Example: * * * * * * * * * * * * *
Input NumberInput rounded to one digit
with {@code UNNECESSARY} rounding *
5.5 throw {@code ArithmeticException}
2.5 throw {@code ArithmeticException}
1.6 throw {@code ArithmeticException}
1.1 throw {@code ArithmeticException}
1.0 1
-1.0 -1
-1.1 throw {@code ArithmeticException}
-1.6 throw {@code ArithmeticException}
-2.5 throw {@code ArithmeticException}
-5.5 throw {@code ArithmeticException}
*/ UNNECESSARY(BigDecimal.ROUND_UNNECESSARY); // Corresponding BigDecimal rounding constant final int oldMode; /** * Constructor * * @param oldMode The {@code BigDecimal} constant corresponding to * this mode */ private RoundingMode(int oldMode) { this.oldMode = oldMode; } /** * Returns the {@code RoundingMode} object corresponding to a * legacy integer rounding mode constant in {@link BigDecimal}. * * @param rm legacy integer rounding mode to convert * @return {@code RoundingMode} corresponding to the given integer. * @throws IllegalArgumentException integer is out of range */ public static RoundingMode valueOf(int rm) { switch(rm) { case BigDecimal.ROUND_UP: return UP; case BigDecimal.ROUND_DOWN: return DOWN; case BigDecimal.ROUND_CEILING: return CEILING; case BigDecimal.ROUND_FLOOR: return FLOOR; case BigDecimal.ROUND_HALF_UP: return HALF_UP; case BigDecimal.ROUND_HALF_DOWN: return HALF_DOWN; case BigDecimal.ROUND_HALF_EVEN: return HALF_EVEN; case BigDecimal.ROUND_UNNECESSARY: return UNNECESSARY; default: throw new IllegalArgumentException("argument out of range"); } } }