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/* * @(#)RoundingMode.java 1.5 06/04/07 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ /* * @(#)RoundingMode.java 1.x 01/xx/xx * * Copyright 2001 Sun Microsystems, Inc. All Rights Reserved. * Portions Copyright IBM Corporation, 2001. All Rights Reserved. * * This software is the proprietary information of Sun Microsystems, Inc. * Use is subject to license terms. * */ package java.math; /** * Specifies a <i>rounding behavior</i> 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 <i>discarded fraction</i> 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. * * <p>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 * <tt>BigDecimal</tt> number with the specified value, forming a * {@link MathContext} object with the proper settings * (<tt>precision</tt> set to <tt>1</tt>, and the * <tt>roundingMode</tt> set to the rounding mode in question), and * calling {@link BigDecimal#round round} on this number with the * proper <tt>MathContext</tt>. A summary table showing the results * of these rounding operations for all rounding modes appears below. * *<p> *<table border> * <caption top><h3>Summary of Rounding Operations Under Different Rounding Modes</h3></caption> * <tr><th></th><th colspan=8>Result of rounding input to one digit with the given * rounding mode</th> * <tr valign=top> * <th>Input Number</th> <th><tt>UP</tt></th> * <th><tt>DOWN</tt></th> * <th><tt>CEILING</tt></th> * <th><tt>FLOOR</tt></th> * <th><tt>HALF_UP</tt></th> * <th><tt>HALF_DOWN</tt></th> * <th><tt>HALF_EVEN</tt></th> * <th><tt>UNNECESSARY</tt></th> * * <tr align=right><td>5.5</td> <td>6</td> <td>5</td> <td>6</td> <td>5</td> <td>6</td> <td>5</td> <td>6</td> <td>throw <tt>ArithmeticException</tt></td> * <tr align=right><td>2.5</td> <td>3</td> <td>2</td> <td>3</td> <td>2</td> <td>3</td> <td>2</td> <td>2</td> <td>throw <tt>ArithmeticException</tt></td> * <tr align=right><td>1.6</td> <td>2</td> <td>1</td> <td>2</td> <td>1</td> <td>2</td> <td>2</td> <td>2</td> <td>throw <tt>ArithmeticException</tt></td> * <tr align=right><td>1.1</td> <td>2</td> <td>1</td> <td>2</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>throw <tt>ArithmeticException</tt></td> * <tr align=right><td>1.0</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> * <tr align=right><td>-1.0</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> * <tr align=right><td>-1.1</td> <td>-2</td> <td>-1</td> <td>-1</td> <td>-2</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>throw <tt>ArithmeticException</tt></td> * <tr align=right><td>-1.6</td> <td>-2</td> <td>-1</td> <td>-1</td> <td>-2</td> <td>-2</td> <td>-2</td> <td>-2</td> <td>throw <tt>ArithmeticException</tt></td> * <tr align=right><td>-2.5</td> <td>-3</td> <td>-2</td> <td>-2</td> <td>-3</td> <td>-3</td> <td>-2</td> <td>-2</td> <td>throw <tt>ArithmeticException</tt></td> * <tr align=right><td>-5.5</td> <td>-6</td> <td>-5</td> <td>-5</td> <td>-6</td> <td>-6</td> <td>-5</td> <td>-6</td> <td>throw <tt>ArithmeticException</tt></td> *</table> * * * <p>This <tt>enum</tt> 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 * @version 1.x 01/xx/xx * @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. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>UP</tt> rounding *<tr align=right><td>5.5</td> <td>6</td> *<tr align=right><td>2.5</td> <td>3</td> *<tr align=right><td>1.6</td> <td>2</td> *<tr align=right><td>1.1</td> <td>2</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-2</td> *<tr align=right><td>-1.6</td> <td>-2</td> *<tr align=right><td>-2.5</td> <td>-3</td> *<tr align=right><td>-5.5</td> <td>-6</td> *</table> */ 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. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>DOWN</tt> rounding *<tr align=right><td>5.5</td> <td>5</td> *<tr align=right><td>2.5</td> <td>2</td> *<tr align=right><td>1.6</td> <td>1</td> *<tr align=right><td>1.1</td> <td>1</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-1</td> *<tr align=right><td>-1.6</td> <td>-1</td> *<tr align=right><td>-2.5</td> <td>-2</td> *<tr align=right><td>-5.5</td> <td>-5</td> *</table> */ DOWN(BigDecimal.ROUND_DOWN), /** * Rounding mode to round towards positive infinity. If the * result is positive, behaves as for <tt>RoundingMode.UP</tt>; * if negative, behaves as for <tt>RoundingMode.DOWN</tt>. Note * that this rounding mode never decreases the calculated value. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>CEILING</tt> rounding *<tr align=right><td>5.5</td> <td>6</td> *<tr align=right><td>2.5</td> <td>3</td> *<tr align=right><td>1.6</td> <td>2</td> *<tr align=right><td>1.1</td> <td>2</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-1</td> *<tr align=right><td>-1.6</td> <td>-1</td> *<tr align=right><td>-2.5</td> <td>-2</td> *<tr align=right><td>-5.5</td> <td>-5</td> *</table> */ CEILING(BigDecimal.ROUND_CEILING), /** * Rounding mode to round towards negative infinity. If the * result is positive, behave as for <tt>RoundingMode.DOWN</tt>; * if negative, behave as for <tt>RoundingMode.UP</tt>. Note that * this rounding mode never increases the calculated value. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>FLOOR</tt> rounding *<tr align=right><td>5.5</td> <td>5</td> *<tr align=right><td>2.5</td> <td>2</td> *<tr align=right><td>1.6</td> <td>1</td> *<tr align=right><td>1.1</td> <td>1</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-2</td> *<tr align=right><td>-1.6</td> <td>-2</td> *<tr align=right><td>-2.5</td> <td>-3</td> *<tr align=right><td>-5.5</td> <td>-6</td> *</table> */ FLOOR(BigDecimal.ROUND_FLOOR), /** * Rounding mode to round towards "nearest neighbor" * unless both neighbors are equidistant, in which case round up. * Behaves as for <tt>RoundingMode.UP</tt> if the discarded * fraction is >= 0.5; otherwise, behaves as for * <tt>RoundingMode.DOWN</tt>. Note that this is the rounding * mode commonly taught at school. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>HALF_UP</tt> rounding *<tr align=right><td>5.5</td> <td>6</td> *<tr align=right><td>2.5</td> <td>3</td> *<tr align=right><td>1.6</td> <td>2</td> *<tr align=right><td>1.1</td> <td>1</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-1</td> *<tr align=right><td>-1.6</td> <td>-2</td> *<tr align=right><td>-2.5</td> <td>-3</td> *<tr align=right><td>-5.5</td> <td>-6</td> *</table> */ HALF_UP(BigDecimal.ROUND_HALF_UP), /** * Rounding mode to round towards "nearest neighbor" * unless both neighbors are equidistant, in which case round * down. Behaves as for <tt>RoundingMode.UP</tt> if the discarded * fraction is > 0.5; otherwise, behaves as for * <tt>RoundingMode.DOWN</tt>. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>HALF_DOWN</tt> rounding *<tr align=right><td>5.5</td> <td>5</td> *<tr align=right><td>2.5</td> <td>2</td> *<tr align=right><td>1.6</td> <td>2</td> *<tr align=right><td>1.1</td> <td>1</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-1</td> *<tr align=right><td>-1.6</td> <td>-2</td> *<tr align=right><td>-2.5</td> <td>-2</td> *<tr align=right><td>-5.5</td> <td>-5</td> *</table> */ HALF_DOWN(BigDecimal.ROUND_HALF_DOWN), /** * Rounding mode to round towards the "nearest neighbor" * unless both neighbors are equidistant, in which case, round * towards the even neighbor. Behaves as for * <tt>RoundingMode.HALF_UP</tt> if the digit to the left of the * discarded fraction is odd; behaves as for * <tt>RoundingMode.HALF_DOWN</tt> 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 <tt>float</tt> and <tt>double</tt> * arithmetic in Java. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>HALF_EVEN</tt> rounding *<tr align=right><td>5.5</td> <td>6</td> *<tr align=right><td>2.5</td> <td>2</td> *<tr align=right><td>1.6</td> <td>2</td> *<tr align=right><td>1.1</td> <td>1</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-1</td> *<tr align=right><td>-1.6</td> <td>-2</td> *<tr align=right><td>-2.5</td> <td>-2</td> *<tr align=right><td>-5.5</td> <td>-6</td> *</table> */ 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 * <tt>ArithmeticException</tt> is thrown. *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>UNNECESSARY</tt> rounding *<tr align=right><td>5.5</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>2.5</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>1.6</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>1.1</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>-1.6</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>-2.5</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>-5.5</td> <td>throw <tt>ArithmeticException</tt></td> *</table> */ UNNECESSARY(BigDecimal.ROUND_UNNECESSARY); // Corresponding BigDecimal rounding constant final int oldMode; /** * Constructor * * @param oldMode The <tt>BigDecimal</tt> constant corresponding to * this mode */ private RoundingMode(int oldMode) { this.oldMode = oldMode; } /** * Returns the <tt>RoundingMode</tt> object corresponding to a * legacy integer rounding mode constant in {@link BigDecimal}. * * @param rm legacy integer rounding mode to convert * @return <tt>RoundingMode</tt> 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"); } } }
