1 /*
2 * Portions Copyright 2003-2007 Sun Microsystems, Inc. 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. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any 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 top><h3>Summary of Rounding Operations Under Different Rounding Modes</h3></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 }
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