1 /*
2 * Copyright (c) 2003, 2017, 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 class="striped">
55 * <caption><b>Summary of Rounding Operations Under Different Rounding Modes</b></caption>
56 * <thead>
57 * <tr><th scope="col" rowspan="2">Input Number</th><th scope="col"colspan=8>Result of rounding input to one digit with the given
58 * rounding mode</th>
59 * <tr style="vertical-align:top">
60 * <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 * </thead>
69 * <tbody style="text-align:right">
70 *
71 * <tr><th scope="row">5.5</th> <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>
72 * <tr><th scope="row">2.5</th> <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>
73 * <tr><th scope="row">1.6</th> <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>
74 * <tr><th scope="row">1.1</th> <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>
75 * <tr><th scope="row">1.0</th> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td>
76 * <tr><th scope="row">-1.0</th> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td>
77 * <tr><th scope="row">-1.1</th> <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>
78 * <tr><th scope="row">-1.6</th> <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>
79 * <tr><th scope="row">-2.5</th> <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>
80 * <tr><th scope="row">-5.5</th> <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>
81 * </tbody>
82 * </table>
83 *
84 *
85 * <p>This {@code enum} is intended to replace the integer-based
86 * enumeration of rounding mode constants in {@link BigDecimal}
87 * ({@link BigDecimal#ROUND_UP}, {@link BigDecimal#ROUND_DOWN},
88 * etc. ).
89 *
90 * @apiNote
91 * Five of the rounding modes defined in this class correspond to
92 * rounding direction attributes defined in IEEE 754-2019. Where
93 * present, this correspondence will be noted in the documentation of
94 * the particular constant.
95 *
96 * @see BigDecimal
97 * @see MathContext
98 * @author Josh Bloch
99 * @author Mike Cowlishaw
100 * @author Joseph D. Darcy
101 * @since 1.5
102 */
103 @SuppressWarnings("deprecation") // Legacy rounding mode constants in BigDecimal
104 public enum RoundingMode {
105
106 /**
107 * Rounding mode to round away from zero. Always increments the
108 * digit prior to a non-zero discarded fraction. Note that this
109 * rounding mode never decreases the magnitude of the calculated
110 * value.
111 *
112 *<p>Example:
113 *<table class="striped">
114 * <caption>Rounding mode UP Examples</caption>
115 *<thead>
116 *<tr style="vertical-align:top"><th scope="col">Input Number</th>
117 * <th scope="col">Input rounded to one digit<br> with {@code UP} rounding
118 *</thead>
119 *<tbody style="text-align:right">
120 *<tr><th scope="row">5.5</th> <td>6</td>
121 *<tr><th scope="row">2.5</th> <td>3</td>
122 *<tr><th scope="row">1.6</th> <td>2</td>
123 *<tr><th scope="row">1.1</th> <td>2</td>
124 *<tr><th scope="row">1.0</th> <td>1</td>
125 *<tr><th scope="row">-1.0</th> <td>-1</td>
126 *<tr><th scope="row">-1.1</th> <td>-2</td>
127 *<tr><th scope="row">-1.6</th> <td>-2</td>
128 *<tr><th scope="row">-2.5</th> <td>-3</td>
129 *<tr><th scope="row">-5.5</th> <td>-6</td>
130 *</tbody>
131 *</table>
132 */
133 UP(BigDecimal.ROUND_UP),
134
135 /**
136 * Rounding mode to round towards zero. Never increments the digit
137 * prior to a discarded fraction (i.e., truncates). Note that this
138 * rounding mode never increases the magnitude of the calculated value.
139 * This mode corresponds to the IEEE 754-2019 rounding
140 * attribute roundTowardZero.
141 *
142 *<p>Example:
143 *<table class="striped">
144 * <caption>Rounding mode DOWN Examples</caption>
145 *<thead>
146 *<tr style="vertical-align:top"><th scope="col">Input Number</th>
147 * <th scope="col">Input rounded to one digit<br> with {@code DOWN} rounding
148 *</thead>
149 *<tbody style="text-align:right">
150 *<tr><th scope="row">5.5</th> <td>5</td>
151 *<tr><th scope="row">2.5</th> <td>2</td>
152 *<tr><th scope="row">1.6</th> <td>1</td>
153 *<tr><th scope="row">1.1</th> <td>1</td>
154 *<tr><th scope="row">1.0</th> <td>1</td>
155 *<tr><th scope="row">-1.0</th> <td>-1</td>
156 *<tr><th scope="row">-1.1</th> <td>-1</td>
157 *<tr><th scope="row">-1.6</th> <td>-1</td>
158 *<tr><th scope="row">-2.5</th> <td>-2</td>
159 *<tr><th scope="row">-5.5</th> <td>-5</td>
160 *</tbody>
161 *</table>
162 */
163 DOWN(BigDecimal.ROUND_DOWN),
164
165 /**
166 * Rounding mode to round towards positive infinity. If the
167 * result is positive, behaves as for {@code RoundingMode.UP};
168 * if negative, behaves as for {@code RoundingMode.DOWN}. Note
169 * that this rounding mode never decreases the calculated value.
170 * This mode corresponds to the IEEE 754-2019 rounding
171 * attribute roundTowardPositive.
172 *
173 *<p>Example:
174 *<table class="striped">
175 * <caption>Rounding mode CEILING Examples</caption>
176 *<thead>
177 *<tr style="vertical-align:top"><th>Input Number</th>
178 * <th>Input rounded to one digit<br> with {@code CEILING} rounding
179 *</thead>
180 *<tbody style="text-align:right">
181 *<tr><th scope="row">5.5</th> <td>6</td>
182 *<tr><th scope="row">2.5</th> <td>3</td>
183 *<tr><th scope="row">1.6</th> <td>2</td>
184 *<tr><th scope="row">1.1</th> <td>2</td>
185 *<tr><th scope="row">1.0</th> <td>1</td>
186 *<tr><th scope="row">-1.0</th> <td>-1</td>
187 *<tr><th scope="row">-1.1</th> <td>-1</td>
188 *<tr><th scope="row">-1.6</th> <td>-1</td>
189 *<tr><th scope="row">-2.5</th> <td>-2</td>
190 *<tr><th scope="row">-5.5</th> <td>-5</td>
191 *</tbody>
192 *</table>
193 */
194 CEILING(BigDecimal.ROUND_CEILING),
195
196 /**
197 * Rounding mode to round towards negative infinity. If the
198 * result is positive, behave as for {@code RoundingMode.DOWN};
199 * if negative, behave as for {@code RoundingMode.UP}. Note that
200 * this rounding mode never increases the calculated value.
201 * This mode corresponds to the IEEE 754-2019 rounding
202 * attribute roundTowardNegative.
203 *
204 *<p>Example:
205 *<table class="striped">
206 * <caption>Rounding mode FLOOR Examples</caption>
207 *<thead>
208 *<tr style="vertical-align:top"><th scope="col">Input Number</th>
209 * <th scope="col">Input rounded to one digit<br> with {@code FLOOR} rounding
210 *</thead>
211 *<tbody style="text-align:right">
212 *<tr><th scope="row">5.5</th> <td>5</td>
213 *<tr><th scope="row">2.5</th> <td>2</td>
214 *<tr><th scope="row">1.6</th> <td>1</td>
215 *<tr><th scope="row">1.1</th> <td>1</td>
216 *<tr><th scope="row">1.0</th> <td>1</td>
217 *<tr><th scope="row">-1.0</th> <td>-1</td>
218 *<tr><th scope="row">-1.1</th> <td>-2</td>
219 *<tr><th scope="row">-1.6</th> <td>-2</td>
220 *<tr><th scope="row">-2.5</th> <td>-3</td>
221 *<tr><th scope="row">-5.5</th> <td>-6</td>
222 *</tbody>
223 *</table>
224 */
225 FLOOR(BigDecimal.ROUND_FLOOR),
226
227 /**
228 * Rounding mode to round towards {@literal "nearest neighbor"}
229 * unless both neighbors are equidistant, in which case round up.
230 * Behaves as for {@code RoundingMode.UP} if the discarded
231 * fraction is ≥ 0.5; otherwise, behaves as for
232 * {@code RoundingMode.DOWN}. Note that this is the rounding
233 * mode commonly taught at school.
234 * This mode corresponds to the IEEE 754-2019 rounding
235 * attribute roundTiesToAway.
236 *
237 *<p>Example:
238 *<table class="striped">
239 * <caption>Rounding mode HALF_UP Examples</caption>
240 *<thead>
241 *<tr style="vertical-align:top"><th scope="col">Input Number</th>
242 * <th scope="col">Input rounded to one digit<br> with {@code HALF_UP} rounding
243 *</thead>
244 *<tbody style="text-align:right">
245 *<tr><th scope="row">5.5</th> <td>6</td>
246 *<tr><th scope="row">2.5</th> <td>3</td>
247 *<tr><th scope="row">1.6</th> <td>2</td>
248 *<tr><th scope="row">1.1</th> <td>1</td>
249 *<tr><th scope="row">1.0</th> <td>1</td>
250 *<tr><th scope="row">-1.0</th> <td>-1</td>
251 *<tr><th scope="row">-1.1</th> <td>-1</td>
252 *<tr><th scope="row">-1.6</th> <td>-2</td>
253 *<tr><th scope="row">-2.5</th> <td>-3</td>
254 *<tr><th scope="row">-5.5</th> <td>-6</td>
255 *</tbody>
256 *</table>
257 */
258 HALF_UP(BigDecimal.ROUND_HALF_UP),
259
260 /**
261 * Rounding mode to round towards {@literal "nearest neighbor"}
262 * unless both neighbors are equidistant, in which case round
263 * down. Behaves as for {@code RoundingMode.UP} if the discarded
264 * fraction is > 0.5; otherwise, behaves as for
265 * {@code RoundingMode.DOWN}.
266 *
267 *<p>Example:
268 *<table class="striped">
269 * <caption>Rounding mode HALF_DOWN Examples</caption>
270 *<thead>
271 *<tr style="vertical-align:top"><th scope="col">Input Number</th>
272 * <th scope="col">Input rounded to one digit<br> with {@code HALF_DOWN} rounding
273 *</thead>
274 *<tbody style="text-align:right">
275 *<tr><th scope="row">5.5</th> <td>5</td>
276 *<tr><th scope="row">2.5</th> <td>2</td>
277 *<tr><th scope="row">1.6</th> <td>2</td>
278 *<tr><th scope="row">1.1</th> <td>1</td>
279 *<tr><th scope="row">1.0</th> <td>1</td>
280 *<tr><th scope="row">-1.0</th> <td>-1</td>
281 *<tr><th scope="row">-1.1</th> <td>-1</td>
282 *<tr><th scope="row">-1.6</th> <td>-2</td>
283 *<tr><th scope="row">-2.5</th> <td>-2</td>
284 *<tr><th scope="row">-5.5</th> <td>-5</td>
285 *</tbody>
286 *</table>
287 */
288 HALF_DOWN(BigDecimal.ROUND_HALF_DOWN),
289
290 /**
291 * Rounding mode to round towards the {@literal "nearest neighbor"}
292 * unless both neighbors are equidistant, in which case, round
293 * towards the even neighbor. Behaves as for
294 * {@code RoundingMode.HALF_UP} if the digit to the left of the
295 * discarded fraction is odd; behaves as for
296 * {@code RoundingMode.HALF_DOWN} if it's even. Note that this
297 * is the rounding mode that statistically minimizes cumulative
298 * error when applied repeatedly over a sequence of calculations.
299 * It is sometimes known as {@literal "Banker's rounding,"} and is
300 * chiefly used in the USA. This rounding mode is analogous to
301 * the rounding policy used for {@code float} and {@code double}
302 * arithmetic in Java.
303 * This mode corresponds to the IEEE 754-2019 rounding
304 * attribute roundTiesToEven.
305 *
306 *<p>Example:
307 *<table class="striped">
308 * <caption>Rounding mode HALF_EVEN Examples</caption>
309 *<thead>
310 *<tr style="vertical-align:top"><th scope="col">Input Number</th>
311 * <th scope="col">Input rounded to one digit<br> with {@code HALF_EVEN} rounding
312 *</thead>
313 *<tbody style="text-align:right">
314 *<tr><th scope="row">5.5</th> <td>6</td>
315 *<tr><th scope="row">2.5</th> <td>2</td>
316 *<tr><th scope="row">1.6</th> <td>2</td>
317 *<tr><th scope="row">1.1</th> <td>1</td>
318 *<tr><th scope="row">1.0</th> <td>1</td>
319 *<tr><th scope="row">-1.0</th> <td>-1</td>
320 *<tr><th scope="row">-1.1</th> <td>-1</td>
321 *<tr><th scope="row">-1.6</th> <td>-2</td>
322 *<tr><th scope="row">-2.5</th> <td>-2</td>
323 *<tr><th scope="row">-5.5</th> <td>-6</td>
324 *</tbody>
325 *</table>
326 */
327 HALF_EVEN(BigDecimal.ROUND_HALF_EVEN),
328
329 /**
330 * Rounding mode to assert that the requested operation has an exact
331 * result, hence no rounding is necessary. If this rounding mode is
332 * specified on an operation that yields an inexact result, an
333 * {@code ArithmeticException} is thrown.
334 *<p>Example:
335 *<table class="striped">
336 * <caption>Rounding mode UNNECESSARY Examples</caption>
337 *<thead>
338 *<tr style="vertical-align:top"><th scope="col">Input Number</th>
339 * <th scope="col">Input rounded to one digit<br> with {@code UNNECESSARY} rounding
340 *</thead>
341 *<tbody style="text-align:right">
342 *<tr><th scope="row">5.5</th> <td>throw {@code ArithmeticException}</td>
343 *<tr><th scope="row">2.5</th> <td>throw {@code ArithmeticException}</td>
344 *<tr><th scope="row">1.6</th> <td>throw {@code ArithmeticException}</td>
345 *<tr><th scope="row">1.1</th> <td>throw {@code ArithmeticException}</td>
346 *<tr><th scope="row">1.0</th> <td>1</td>
347 *<tr><th scope="row">-1.0</th> <td>-1</td>
348 *<tr><th scope="row">-1.1</th> <td>throw {@code ArithmeticException}</td>
349 *<tr><th scope="row">-1.6</th> <td>throw {@code ArithmeticException}</td>
350 *<tr><th scope="row">-2.5</th> <td>throw {@code ArithmeticException}</td>
351 *<tr><th scope="row">-5.5</th> <td>throw {@code ArithmeticException}</td>
352 *</tbody>
353 *</table>
354 */
355 UNNECESSARY(BigDecimal.ROUND_UNNECESSARY);
356
357 // Corresponding BigDecimal rounding constant
358 final int oldMode;
359
360 /**
361 * Constructor
362 *
363 * @param oldMode The {@code BigDecimal} constant corresponding to
364 * this mode
365 */
366 private RoundingMode(int oldMode) {
367 this.oldMode = oldMode;
368 }
369
370 /**
371 * Returns the {@code RoundingMode} object corresponding to a
372 * legacy integer rounding mode constant in {@link BigDecimal}.
373 *
374 * @param rm legacy integer rounding mode to convert
375 * @return {@code RoundingMode} corresponding to the given integer.
376 * @throws IllegalArgumentException integer is out of range
377 */
378 public static RoundingMode valueOf(int rm) {
379 switch(rm) {
380
381 case BigDecimal.ROUND_UP:
382 return UP;
383
384 case BigDecimal.ROUND_DOWN:
385 return DOWN;
386
387 case BigDecimal.ROUND_CEILING:
388 return CEILING;
389
390 case BigDecimal.ROUND_FLOOR:
391 return FLOOR;
392
393 case BigDecimal.ROUND_HALF_UP:
394 return HALF_UP;
395
396 case BigDecimal.ROUND_HALF_DOWN:
397 return HALF_DOWN;
398
399 case BigDecimal.ROUND_HALF_EVEN:
400 return HALF_EVEN;
401
402 case BigDecimal.ROUND_UNNECESSARY:
403 return UNNECESSARY;
404
405 default:
406 throw new IllegalArgumentException("argument out of range");
407 }
408 }
409 }