1 /* 2 * Copyright (c) 2003, 2011, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 /* 27 * Portions Copyright IBM Corporation, 2001. All Rights Reserved. 28 */ 29 package java.math; 30 31 /** 32 * Specifies a <i>rounding behavior</i> for numerical operations 33 * capable of discarding precision. Each rounding mode indicates how 34 * the least significant returned digit of a rounded result is to be 35 * calculated. If fewer digits are returned than the digits needed to 36 * represent the exact numerical result, the discarded digits will be 37 * referred to as the <i>discarded fraction</i> regardless the digits' 38 * contribution to the value of the number. In other words, 39 * considered as a numerical value, the discarded fraction could have 40 * an absolute value greater than one. 41 * 42 * <p>Each rounding mode description includes a table listing how 43 * different two-digit decimal values would round to a one digit 44 * decimal value under the rounding mode in question. The result 45 * column in the tables could be gotten by creating a 46 * {@code BigDecimal} number with the specified value, forming a 47 * {@link MathContext} object with the proper settings 48 * ({@code precision} set to {@code 1}, and the 49 * {@code roundingMode} set to the rounding mode in question), and 50 * calling {@link BigDecimal#round round} on this number with the 51 * proper {@code MathContext}. A summary table showing the results 52 * of these rounding operations for all rounding modes appears below. 53 * 54 *<p> 55 *<table border> 56 * <caption><b>Summary of Rounding Operations Under Different Rounding Modes</b></caption> 57 * <tr><th></th><th colspan=8>Result of rounding input to one digit with the given 58 * rounding mode</th> 59 * <tr valign=top> 60 * <th>Input Number</th> <th>{@code UP}</th> 61 * <th>{@code DOWN}</th> 62 * <th>{@code CEILING}</th> 63 * <th>{@code FLOOR}</th> 64 * <th>{@code HALF_UP}</th> 65 * <th>{@code HALF_DOWN}</th> 66 * <th>{@code HALF_EVEN}</th> 67 * <th>{@code UNNECESSARY}</th> 68 * 69 * <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 {@code ArithmeticException}</td> 70 * <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 {@code ArithmeticException}</td> 71 * <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 {@code ArithmeticException}</td> 72 * <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 {@code ArithmeticException}</td> 73 * <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> 74 * <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> 75 * <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 {@code ArithmeticException}</td> 76 * <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 {@code ArithmeticException}</td> 77 * <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 {@code ArithmeticException}</td> 78 * <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 {@code ArithmeticException}</td> 79 *</table> 80 * 81 * 82 * <p>This {@code enum} is intended to replace the integer-based 83 * enumeration of rounding mode constants in {@link BigDecimal} 84 * ({@link BigDecimal#ROUND_UP}, {@link BigDecimal#ROUND_DOWN}, 85 * etc. ). 86 * 87 * @see BigDecimal 88 * @see MathContext 89 * @author Josh Bloch 90 * @author Mike Cowlishaw 91 * @author Joseph D. Darcy 92 * @since 1.5 93 */ 94 public enum RoundingMode { 95 96 /** 97 * Rounding mode to round away from zero. Always increments the 98 * digit prior to a non-zero discarded fraction. Note that this 99 * rounding mode never decreases the magnitude of the calculated 100 * value. 101 * 102 *<p>Example: 103 *<table border> 104 *<tr valign=top><th>Input Number</th> 105 * <th>Input rounded to one digit<br> with {@code UP} rounding 106 *<tr align=right><td>5.5</td> <td>6</td> 107 *<tr align=right><td>2.5</td> <td>3</td> 108 *<tr align=right><td>1.6</td> <td>2</td> 109 *<tr align=right><td>1.1</td> <td>2</td> 110 *<tr align=right><td>1.0</td> <td>1</td> 111 *<tr align=right><td>-1.0</td> <td>-1</td> 112 *<tr align=right><td>-1.1</td> <td>-2</td> 113 *<tr align=right><td>-1.6</td> <td>-2</td> 114 *<tr align=right><td>-2.5</td> <td>-3</td> 115 *<tr align=right><td>-5.5</td> <td>-6</td> 116 *</table> 117 */ 118 UP(BigDecimal.ROUND_UP), 119 120 /** 121 * Rounding mode to round towards zero. Never increments the digit 122 * prior to a discarded fraction (i.e., truncates). Note that this 123 * rounding mode never increases the magnitude of the calculated value. 124 * 125 *<p>Example: 126 *<table border> 127 *<tr valign=top><th>Input Number</th> 128 * <th>Input rounded to one digit<br> with {@code DOWN} rounding 129 *<tr align=right><td>5.5</td> <td>5</td> 130 *<tr align=right><td>2.5</td> <td>2</td> 131 *<tr align=right><td>1.6</td> <td>1</td> 132 *<tr align=right><td>1.1</td> <td>1</td> 133 *<tr align=right><td>1.0</td> <td>1</td> 134 *<tr align=right><td>-1.0</td> <td>-1</td> 135 *<tr align=right><td>-1.1</td> <td>-1</td> 136 *<tr align=right><td>-1.6</td> <td>-1</td> 137 *<tr align=right><td>-2.5</td> <td>-2</td> 138 *<tr align=right><td>-5.5</td> <td>-5</td> 139 *</table> 140 */ 141 DOWN(BigDecimal.ROUND_DOWN), 142 143 /** 144 * Rounding mode to round towards positive infinity. If the 145 * result is positive, behaves as for {@code RoundingMode.UP}; 146 * if negative, behaves as for {@code RoundingMode.DOWN}. Note 147 * that this rounding mode never decreases the calculated value. 148 * 149 *<p>Example: 150 *<table border> 151 *<tr valign=top><th>Input Number</th> 152 * <th>Input rounded to one digit<br> with {@code CEILING} rounding 153 *<tr align=right><td>5.5</td> <td>6</td> 154 *<tr align=right><td>2.5</td> <td>3</td> 155 *<tr align=right><td>1.6</td> <td>2</td> 156 *<tr align=right><td>1.1</td> <td>2</td> 157 *<tr align=right><td>1.0</td> <td>1</td> 158 *<tr align=right><td>-1.0</td> <td>-1</td> 159 *<tr align=right><td>-1.1</td> <td>-1</td> 160 *<tr align=right><td>-1.6</td> <td>-1</td> 161 *<tr align=right><td>-2.5</td> <td>-2</td> 162 *<tr align=right><td>-5.5</td> <td>-5</td> 163 *</table> 164 */ 165 CEILING(BigDecimal.ROUND_CEILING), 166 167 /** 168 * Rounding mode to round towards negative infinity. If the 169 * result is positive, behave as for {@code RoundingMode.DOWN}; 170 * if negative, behave as for {@code RoundingMode.UP}. Note that 171 * this rounding mode never increases the calculated value. 172 * 173 *<p>Example: 174 *<table border> 175 *<tr valign=top><th>Input Number</th> 176 * <th>Input rounded to one digit<br> with {@code FLOOR} rounding 177 *<tr align=right><td>5.5</td> <td>5</td> 178 *<tr align=right><td>2.5</td> <td>2</td> 179 *<tr align=right><td>1.6</td> <td>1</td> 180 *<tr align=right><td>1.1</td> <td>1</td> 181 *<tr align=right><td>1.0</td> <td>1</td> 182 *<tr align=right><td>-1.0</td> <td>-1</td> 183 *<tr align=right><td>-1.1</td> <td>-2</td> 184 *<tr align=right><td>-1.6</td> <td>-2</td> 185 *<tr align=right><td>-2.5</td> <td>-3</td> 186 *<tr align=right><td>-5.5</td> <td>-6</td> 187 *</table> 188 */ 189 FLOOR(BigDecimal.ROUND_FLOOR), 190 191 /** 192 * Rounding mode to round towards {@literal "nearest neighbor"} 193 * unless both neighbors are equidistant, in which case round up. 194 * Behaves as for {@code RoundingMode.UP} if the discarded 195 * fraction is ≥ 0.5; otherwise, behaves as for 196 * {@code RoundingMode.DOWN}. Note that this is the rounding 197 * mode commonly taught at school. 198 * 199 *<p>Example: 200 *<table border> 201 *<tr valign=top><th>Input Number</th> 202 * <th>Input rounded to one digit<br> with {@code HALF_UP} rounding 203 *<tr align=right><td>5.5</td> <td>6</td> 204 *<tr align=right><td>2.5</td> <td>3</td> 205 *<tr align=right><td>1.6</td> <td>2</td> 206 *<tr align=right><td>1.1</td> <td>1</td> 207 *<tr align=right><td>1.0</td> <td>1</td> 208 *<tr align=right><td>-1.0</td> <td>-1</td> 209 *<tr align=right><td>-1.1</td> <td>-1</td> 210 *<tr align=right><td>-1.6</td> <td>-2</td> 211 *<tr align=right><td>-2.5</td> <td>-3</td> 212 *<tr align=right><td>-5.5</td> <td>-6</td> 213 *</table> 214 */ 215 HALF_UP(BigDecimal.ROUND_HALF_UP), 216 217 /** 218 * Rounding mode to round towards {@literal "nearest neighbor"} 219 * unless both neighbors are equidistant, in which case round 220 * down. Behaves as for {@code RoundingMode.UP} if the discarded 221 * fraction is > 0.5; otherwise, behaves as for 222 * {@code RoundingMode.DOWN}. 223 * 224 *<p>Example: 225 *<table border> 226 *<tr valign=top><th>Input Number</th> 227 * <th>Input rounded to one digit<br> with {@code HALF_DOWN} rounding 228 *<tr align=right><td>5.5</td> <td>5</td> 229 *<tr align=right><td>2.5</td> <td>2</td> 230 *<tr align=right><td>1.6</td> <td>2</td> 231 *<tr align=right><td>1.1</td> <td>1</td> 232 *<tr align=right><td>1.0</td> <td>1</td> 233 *<tr align=right><td>-1.0</td> <td>-1</td> 234 *<tr align=right><td>-1.1</td> <td>-1</td> 235 *<tr align=right><td>-1.6</td> <td>-2</td> 236 *<tr align=right><td>-2.5</td> <td>-2</td> 237 *<tr align=right><td>-5.5</td> <td>-5</td> 238 *</table> 239 */ 240 HALF_DOWN(BigDecimal.ROUND_HALF_DOWN), 241 242 /** 243 * Rounding mode to round towards the {@literal "nearest neighbor"} 244 * unless both neighbors are equidistant, in which case, round 245 * towards the even neighbor. Behaves as for 246 * {@code RoundingMode.HALF_UP} if the digit to the left of the 247 * discarded fraction is odd; behaves as for 248 * {@code RoundingMode.HALF_DOWN} if it's even. Note that this 249 * is the rounding mode that statistically minimizes cumulative 250 * error when applied repeatedly over a sequence of calculations. 251 * It is sometimes known as {@literal "Banker's rounding,"} and is 252 * chiefly used in the USA. This rounding mode is analogous to 253 * the rounding policy used for {@code float} and {@code double} 254 * arithmetic in Java. 255 * 256 *<p>Example: 257 *<table border> 258 *<tr valign=top><th>Input Number</th> 259 * <th>Input rounded to one digit<br> with {@code HALF_EVEN} rounding 260 *<tr align=right><td>5.5</td> <td>6</td> 261 *<tr align=right><td>2.5</td> <td>2</td> 262 *<tr align=right><td>1.6</td> <td>2</td> 263 *<tr align=right><td>1.1</td> <td>1</td> 264 *<tr align=right><td>1.0</td> <td>1</td> 265 *<tr align=right><td>-1.0</td> <td>-1</td> 266 *<tr align=right><td>-1.1</td> <td>-1</td> 267 *<tr align=right><td>-1.6</td> <td>-2</td> 268 *<tr align=right><td>-2.5</td> <td>-2</td> 269 *<tr align=right><td>-5.5</td> <td>-6</td> 270 *</table> 271 */ 272 HALF_EVEN(BigDecimal.ROUND_HALF_EVEN), 273 274 /** 275 * Rounding mode to assert that the requested operation has an exact 276 * result, hence no rounding is necessary. If this rounding mode is 277 * specified on an operation that yields an inexact result, an 278 * {@code ArithmeticException} is thrown. 279 *<p>Example: 280 *<table border> 281 *<tr valign=top><th>Input Number</th> 282 * <th>Input rounded to one digit<br> with {@code UNNECESSARY} rounding 283 *<tr align=right><td>5.5</td> <td>throw {@code ArithmeticException}</td> 284 *<tr align=right><td>2.5</td> <td>throw {@code ArithmeticException}</td> 285 *<tr align=right><td>1.6</td> <td>throw {@code ArithmeticException}</td> 286 *<tr align=right><td>1.1</td> <td>throw {@code ArithmeticException}</td> 287 *<tr align=right><td>1.0</td> <td>1</td> 288 *<tr align=right><td>-1.0</td> <td>-1</td> 289 *<tr align=right><td>-1.1</td> <td>throw {@code ArithmeticException}</td> 290 *<tr align=right><td>-1.6</td> <td>throw {@code ArithmeticException}</td> 291 *<tr align=right><td>-2.5</td> <td>throw {@code ArithmeticException}</td> 292 *<tr align=right><td>-5.5</td> <td>throw {@code ArithmeticException}</td> 293 *</table> 294 */ 295 UNNECESSARY(BigDecimal.ROUND_UNNECESSARY); 296 297 // Corresponding BigDecimal rounding constant 298 final int oldMode; 299 300 /** 301 * Constructor 302 * 303 * @param oldMode The {@code BigDecimal} constant corresponding to 304 * this mode 305 */ 306 private RoundingMode(int oldMode) { 307 this.oldMode = oldMode; 308 } 309 310 /** 311 * Returns the {@code RoundingMode} object corresponding to a 312 * legacy integer rounding mode constant in {@link BigDecimal}. 313 * 314 * @param rm legacy integer rounding mode to convert 315 * @return {@code RoundingMode} corresponding to the given integer. 316 * @throws IllegalArgumentException integer is out of range 317 */ 318 public static RoundingMode valueOf(int rm) { 319 switch(rm) { 320 321 case BigDecimal.ROUND_UP: 322 return UP; 323 324 case BigDecimal.ROUND_DOWN: 325 return DOWN; 326 327 case BigDecimal.ROUND_CEILING: 328 return CEILING; 329 330 case BigDecimal.ROUND_FLOOR: 331 return FLOOR; 332 333 case BigDecimal.ROUND_HALF_UP: 334 return HALF_UP; 335 336 case BigDecimal.ROUND_HALF_DOWN: 337 return HALF_DOWN; 338 339 case BigDecimal.ROUND_HALF_EVEN: 340 return HALF_EVEN; 341 342 case BigDecimal.ROUND_UNNECESSARY: 343 return UNNECESSARY; 344 345 default: 346 throw new IllegalArgumentException("argument out of range"); 347 } 348 } 349 }