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