1 /* 2 * Copyright (c) 2003, 2013, 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 *<table border> 55 * <caption><b>Summary of Rounding Operations Under Different Rounding Modes</b></caption> 56 * <tr><th></th><th colspan=8>Result of rounding input to one digit with the given 57 * rounding mode</th> 58 * <tr valign=top> 59 * <th>Input Number</th> <th>{@code UP}</th> 60 * <th>{@code DOWN}</th> 61 * <th>{@code CEILING}</th> 62 * <th>{@code FLOOR}</th> 63 * <th>{@code HALF_UP}</th> 64 * <th>{@code HALF_DOWN}</th> 65 * <th>{@code HALF_EVEN}</th> 66 * <th>{@code UNNECESSARY}</th> 67 * 68 * <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> 69 * <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> 70 * <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> 71 * <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> 72 * <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> 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>-1.1</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> 75 * <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> 76 * <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> 77 * <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> 78 *</table> 79 * 80 * 81 * <p>This {@code enum} is intended to replace the integer-based 82 * enumeration of rounding mode constants in {@link BigDecimal} 83 * ({@link BigDecimal#ROUND_UP}, {@link BigDecimal#ROUND_DOWN}, 84 * etc. ). 85 * 86 * @see BigDecimal 87 * @see MathContext 88 * @author Josh Bloch 89 * @author Mike Cowlishaw 90 * @author Joseph D. Darcy 91 * @since 1.5 92 */ 93 public enum RoundingMode { 94 95 /** 96 * Rounding mode to round away from zero. Always increments the 97 * digit prior to a non-zero discarded fraction. Note that this 98 * rounding mode never decreases the magnitude of the calculated 99 * value. 100 * 101 *<p>Example: 102 *<table border> 103 * <caption><b>Rounding mode UP Examples</b></caption> 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 * <caption><b>Rounding mode DOWN Examples</b></caption> 128 *<tr valign=top><th>Input Number</th> 129 * <th>Input rounded to one digit<br> with {@code DOWN} rounding 130 *<tr align=right><td>5.5</td> <td>5</td> 131 *<tr align=right><td>2.5</td> <td>2</td> 132 *<tr align=right><td>1.6</td> <td>1</td> 133 *<tr align=right><td>1.1</td> <td>1</td> 134 *<tr align=right><td>1.0</td> <td>1</td> 135 *<tr align=right><td>-1.0</td> <td>-1</td> 136 *<tr align=right><td>-1.1</td> <td>-1</td> 137 *<tr align=right><td>-1.6</td> <td>-1</td> 138 *<tr align=right><td>-2.5</td> <td>-2</td> 139 *<tr align=right><td>-5.5</td> <td>-5</td> 140 *</table> 141 */ 142 DOWN(BigDecimal.ROUND_DOWN), 143 144 /** 145 * Rounding mode to round towards positive infinity. If the 146 * result is positive, behaves as for {@code RoundingMode.UP}; 147 * if negative, behaves as for {@code RoundingMode.DOWN}. Note 148 * that this rounding mode never decreases the calculated value. 149 * 150 *<p>Example: 151 *<table border> 152 * <caption><b>Rounding mode CEILING Examples</b></caption> 153 *<tr valign=top><th>Input Number</th> 154 * <th>Input rounded to one digit<br> with {@code CEILING} rounding 155 *<tr align=right><td>5.5</td> <td>6</td> 156 *<tr align=right><td>2.5</td> <td>3</td> 157 *<tr align=right><td>1.6</td> <td>2</td> 158 *<tr align=right><td>1.1</td> <td>2</td> 159 *<tr align=right><td>1.0</td> <td>1</td> 160 *<tr align=right><td>-1.0</td> <td>-1</td> 161 *<tr align=right><td>-1.1</td> <td>-1</td> 162 *<tr align=right><td>-1.6</td> <td>-1</td> 163 *<tr align=right><td>-2.5</td> <td>-2</td> 164 *<tr align=right><td>-5.5</td> <td>-5</td> 165 *</table> 166 */ 167 CEILING(BigDecimal.ROUND_CEILING), 168 169 /** 170 * Rounding mode to round towards negative infinity. If the 171 * result is positive, behave as for {@code RoundingMode.DOWN}; 172 * if negative, behave as for {@code RoundingMode.UP}. Note that 173 * this rounding mode never increases the calculated value. 174 * 175 *<p>Example: 176 *<table border> 177 * <caption><b>Rounding mode FLOOR Examples</b></caption> 178 *<tr valign=top><th>Input Number</th> 179 * <th>Input rounded to one digit<br> with {@code FLOOR} rounding 180 *<tr align=right><td>5.5</td> <td>5</td> 181 *<tr align=right><td>2.5</td> <td>2</td> 182 *<tr align=right><td>1.6</td> <td>1</td> 183 *<tr align=right><td>1.1</td> <td>1</td> 184 *<tr align=right><td>1.0</td> <td>1</td> 185 *<tr align=right><td>-1.0</td> <td>-1</td> 186 *<tr align=right><td>-1.1</td> <td>-2</td> 187 *<tr align=right><td>-1.6</td> <td>-2</td> 188 *<tr align=right><td>-2.5</td> <td>-3</td> 189 *<tr align=right><td>-5.5</td> <td>-6</td> 190 *</table> 191 */ 192 FLOOR(BigDecimal.ROUND_FLOOR), 193 194 /** 195 * Rounding mode to round towards {@literal "nearest neighbor"} 196 * unless both neighbors are equidistant, in which case round up. 197 * Behaves as for {@code RoundingMode.UP} if the discarded 198 * fraction is ≥ 0.5; otherwise, behaves as for 199 * {@code RoundingMode.DOWN}. Note that this is the rounding 200 * mode commonly taught at school. 201 * 202 *<p>Example: 203 *<table border> 204 * <caption><b>Rounding mode HALF_UP Examples</b></caption> 205 *<tr valign=top><th>Input Number</th> 206 * <th>Input rounded to one digit<br> with {@code HALF_UP} rounding 207 *<tr align=right><td>5.5</td> <td>6</td> 208 *<tr align=right><td>2.5</td> <td>3</td> 209 *<tr align=right><td>1.6</td> <td>2</td> 210 *<tr align=right><td>1.1</td> <td>1</td> 211 *<tr align=right><td>1.0</td> <td>1</td> 212 *<tr align=right><td>-1.0</td> <td>-1</td> 213 *<tr align=right><td>-1.1</td> <td>-1</td> 214 *<tr align=right><td>-1.6</td> <td>-2</td> 215 *<tr align=right><td>-2.5</td> <td>-3</td> 216 *<tr align=right><td>-5.5</td> <td>-6</td> 217 *</table> 218 */ 219 HALF_UP(BigDecimal.ROUND_HALF_UP), 220 221 /** 222 * Rounding mode to round towards {@literal "nearest neighbor"} 223 * unless both neighbors are equidistant, in which case round 224 * down. Behaves as for {@code RoundingMode.UP} if the discarded 225 * fraction is > 0.5; otherwise, behaves as for 226 * {@code RoundingMode.DOWN}. 227 * 228 *<p>Example: 229 *<table border> 230 * <caption><b>Rounding mode HALF_DOWN Examples</b></caption> 231 *<tr valign=top><th>Input Number</th> 232 * <th>Input rounded to one digit<br> with {@code HALF_DOWN} rounding 233 *<tr align=right><td>5.5</td> <td>5</td> 234 *<tr align=right><td>2.5</td> <td>2</td> 235 *<tr align=right><td>1.6</td> <td>2</td> 236 *<tr align=right><td>1.1</td> <td>1</td> 237 *<tr align=right><td>1.0</td> <td>1</td> 238 *<tr align=right><td>-1.0</td> <td>-1</td> 239 *<tr align=right><td>-1.1</td> <td>-1</td> 240 *<tr align=right><td>-1.6</td> <td>-2</td> 241 *<tr align=right><td>-2.5</td> <td>-2</td> 242 *<tr align=right><td>-5.5</td> <td>-5</td> 243 *</table> 244 */ 245 HALF_DOWN(BigDecimal.ROUND_HALF_DOWN), 246 247 /** 248 * Rounding mode to round towards the {@literal "nearest neighbor"} 249 * unless both neighbors are equidistant, in which case, round 250 * towards the even neighbor. Behaves as for 251 * {@code RoundingMode.HALF_UP} if the digit to the left of the 252 * discarded fraction is odd; behaves as for 253 * {@code RoundingMode.HALF_DOWN} if it's even. Note that this 254 * is the rounding mode that statistically minimizes cumulative 255 * error when applied repeatedly over a sequence of calculations. 256 * It is sometimes known as {@literal "Banker's rounding,"} and is 257 * chiefly used in the USA. This rounding mode is analogous to 258 * the rounding policy used for {@code float} and {@code double} 259 * arithmetic in Java. 260 * 261 *<p>Example: 262 *<table border> 263 * <caption><b>Rounding mode HALF_EVEN Examples</b></caption> 264 *<tr valign=top><th>Input Number</th> 265 * <th>Input rounded to one digit<br> with {@code HALF_EVEN} rounding 266 *<tr align=right><td>5.5</td> <td>6</td> 267 *<tr align=right><td>2.5</td> <td>2</td> 268 *<tr align=right><td>1.6</td> <td>2</td> 269 *<tr align=right><td>1.1</td> <td>1</td> 270 *<tr align=right><td>1.0</td> <td>1</td> 271 *<tr align=right><td>-1.0</td> <td>-1</td> 272 *<tr align=right><td>-1.1</td> <td>-1</td> 273 *<tr align=right><td>-1.6</td> <td>-2</td> 274 *<tr align=right><td>-2.5</td> <td>-2</td> 275 *<tr align=right><td>-5.5</td> <td>-6</td> 276 *</table> 277 */ 278 HALF_EVEN(BigDecimal.ROUND_HALF_EVEN), 279 280 /** 281 * Rounding mode to assert that the requested operation has an exact 282 * result, hence no rounding is necessary. If this rounding mode is 283 * specified on an operation that yields an inexact result, an 284 * {@code ArithmeticException} is thrown. 285 *<p>Example: 286 *<table border> 287 * <caption><b>Rounding mode UNNECESSARY Examples</b></caption> 288 *<tr valign=top><th>Input Number</th> 289 * <th>Input rounded to one digit<br> with {@code UNNECESSARY} rounding 290 *<tr align=right><td>5.5</td> <td>throw {@code ArithmeticException}</td> 291 *<tr align=right><td>2.5</td> <td>throw {@code ArithmeticException}</td> 292 *<tr align=right><td>1.6</td> <td>throw {@code ArithmeticException}</td> 293 *<tr align=right><td>1.1</td> <td>throw {@code ArithmeticException}</td> 294 *<tr align=right><td>1.0</td> <td>1</td> 295 *<tr align=right><td>-1.0</td> <td>-1</td> 296 *<tr align=right><td>-1.1</td> <td>throw {@code ArithmeticException}</td> 297 *<tr align=right><td>-1.6</td> <td>throw {@code ArithmeticException}</td> 298 *<tr align=right><td>-2.5</td> <td>throw {@code ArithmeticException}</td> 299 *<tr align=right><td>-5.5</td> <td>throw {@code ArithmeticException}</td> 300 *</table> 301 */ 302 UNNECESSARY(BigDecimal.ROUND_UNNECESSARY); 303 304 // Corresponding BigDecimal rounding constant 305 final int oldMode; 306 307 /** 308 * Constructor 309 * 310 * @param oldMode The {@code BigDecimal} constant corresponding to 311 * this mode 312 */ RoundingMode(int oldMode)313 private RoundingMode(int oldMode) { 314 this.oldMode = oldMode; 315 } 316 317 /** 318 * Returns the {@code RoundingMode} object corresponding to a 319 * legacy integer rounding mode constant in {@link BigDecimal}. 320 * 321 * @param rm legacy integer rounding mode to convert 322 * @return {@code RoundingMode} corresponding to the given integer. 323 * @throws IllegalArgumentException integer is out of range 324 */ valueOf(int rm)325 public static RoundingMode valueOf(int rm) { 326 switch(rm) { 327 328 case BigDecimal.ROUND_UP: 329 return UP; 330 331 case BigDecimal.ROUND_DOWN: 332 return DOWN; 333 334 case BigDecimal.ROUND_CEILING: 335 return CEILING; 336 337 case BigDecimal.ROUND_FLOOR: 338 return FLOOR; 339 340 case BigDecimal.ROUND_HALF_UP: 341 return HALF_UP; 342 343 case BigDecimal.ROUND_HALF_DOWN: 344 return HALF_DOWN; 345 346 case BigDecimal.ROUND_HALF_EVEN: 347 return HALF_EVEN; 348 349 case BigDecimal.ROUND_UNNECESSARY: 350 return UNNECESSARY; 351 352 default: 353 throw new IllegalArgumentException("argument out of range"); 354 } 355 } 356 } 357