1 /*
2 * Copyright (c) 2003, 2007, 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, 1997, 2001. All Rights Reserved.
28 */
29
30 package java.math;
31 import java.io.*;
32
33 /**
34 * Immutable objects which encapsulate the context settings which
35 * describe certain rules for numerical operators, such as those
36 * implemented by the {@link BigDecimal} class.
37 *
38 * <p>The base-independent settings are:
39 * <ol>
40 * <li>{@code precision}:
41 * the number of digits to be used for an operation; results are
42 * rounded to this precision
43 *
44 * <li>{@code roundingMode}:
45 * a {@link RoundingMode} object which specifies the algorithm to be
46 * used for rounding.
47 * </ol>
48 *
49 * @see BigDecimal
50 * @see RoundingMode
51 * @author Mike Cowlishaw
52 * @author Joseph D. Darcy
53 * @since 1.5
54 */
55
56 public final class MathContext implements Serializable {
57
58 /* ----- Constants ----- */
59
60 // defaults for constructors
61 private static final int DEFAULT_DIGITS = 9;
62 private static final RoundingMode DEFAULT_ROUNDINGMODE = RoundingMode.HALF_UP;
63 // Smallest values for digits (Maximum is Integer.MAX_VALUE)
64 private static final int MIN_DIGITS = 0;
65
66 // Serialization version
67 private static final long serialVersionUID = 5579720004786848255L;
68
69 /* ----- Public Properties ----- */
70 /**
71 * A {@code MathContext} object whose settings have the values
72 * required for unlimited precision arithmetic.
73 * The values of the settings are:
74 * <code>
75 * precision=0 roundingMode=HALF_UP
76 * </code>
77 */
78 public static final MathContext UNLIMITED =
79 new MathContext(0, RoundingMode.HALF_UP);
80
81 /**
82 * A {@code MathContext} object with a precision setting
83 * matching the IEEE 754R Decimal32 format, 7 digits, and a
84 * rounding mode of {@link RoundingMode#HALF_EVEN HALF_EVEN}, the
85 * IEEE 754R default.
86 */
87 public static final MathContext DECIMAL32 =
88 new MathContext(7, RoundingMode.HALF_EVEN);
89
90 /**
91 * A {@code MathContext} object with a precision setting
92 * matching the IEEE 754R Decimal64 format, 16 digits, and a
93 * rounding mode of {@link RoundingMode#HALF_EVEN HALF_EVEN}, the
94 * IEEE 754R default.
95 */
96 public static final MathContext DECIMAL64 =
97 new MathContext(16, RoundingMode.HALF_EVEN);
98
99 /**
100 * A {@code MathContext} object with a precision setting
101 * matching the IEEE 754R Decimal128 format, 34 digits, and a
102 * rounding mode of {@link RoundingMode#HALF_EVEN HALF_EVEN}, the
103 * IEEE 754R default.
104 */
105 public static final MathContext DECIMAL128 =
106 new MathContext(34, RoundingMode.HALF_EVEN);
107
108 /* ----- Shared Properties ----- */
109 /**
110 * The number of digits to be used for an operation. A value of 0
111 * indicates that unlimited precision (as many digits as are
112 * required) will be used. Note that leading zeros (in the
113 * coefficient of a number) are never significant.
114 *
115 * <p>{@code precision} will always be non-negative.
116 *
117 * @serial
118 */
119 final int precision;
120
121 /**
122 * The rounding algorithm to be used for an operation.
123 *
124 * @see RoundingMode
125 * @serial
126 */
127 final RoundingMode roundingMode;
128
129 /* ----- Constructors ----- */
130
131 /**
132 * Constructs a new {@code MathContext} with the specified
133 * precision and the {@link RoundingMode#HALF_UP HALF_UP} rounding
134 * mode.
135 *
136 * @param setPrecision The non-negative {@code int} precision setting.
137 * @throws IllegalArgumentException if the {@code setPrecision} parameter is less
138 * than zero.
139 */
140 public MathContext(int setPrecision) {
141 this(setPrecision, DEFAULT_ROUNDINGMODE);
142 return;
143 }
144
145 /**
146 * Constructs a new {@code MathContext} with a specified
147 * precision and rounding mode.
148 *
149 * @param setPrecision The non-negative {@code int} precision setting.
150 * @param setRoundingMode The rounding mode to use.
151 * @throws IllegalArgumentException if the {@code setPrecision} parameter is less
152 * than zero.
153 * @throws NullPointerException if the rounding mode argument is {@code null}
154 */
155 public MathContext(int setPrecision,
156 RoundingMode setRoundingMode) {
157 if (setPrecision < MIN_DIGITS)
158 throw new IllegalArgumentException("Digits < 0");
159 if (setRoundingMode == null)
160 throw new NullPointerException("null RoundingMode");
161
162 precision = setPrecision;
163 roundingMode = setRoundingMode;
164 return;
165 }
166
167 /**
168 * Constructs a new {@code MathContext} from a string.
169 *
170 * The string must be in the same format as that produced by the
171 * {@link #toString} method.
172 *
173 * <p>An {@code IllegalArgumentException} is thrown if the precision
174 * section of the string is out of range ({@code < 0}) or the string is
175 * not in the format created by the {@link #toString} method.
176 *
177 * @param val The string to be parsed
178 * @throws IllegalArgumentException if the precision section is out of range
179 * or of incorrect format
180 * @throws NullPointerException if the argument is {@code null}
181 */
182 public MathContext(String val) {
183 boolean bad = false;
184 int setPrecision;
185 if (val == null)
186 throw new NullPointerException("null String");
187 try { // any error here is a string format problem
188 if (!val.startsWith("precision=")) throw new RuntimeException();
189 int fence = val.indexOf(' '); // could be -1
190 int off = 10; // where value starts
191 setPrecision = Integer.parseInt(val.substring(10, fence));
192
193 if (!val.startsWith("roundingMode=", fence+1))
194 throw new RuntimeException();
195 off = fence + 1 + 13;
196 String str = val.substring(off, val.length());
197 roundingMode = RoundingMode.valueOf(str);
198 } catch (RuntimeException re) {
199 throw new IllegalArgumentException("bad string format");
200 }
201
202 if (setPrecision < MIN_DIGITS)
203 throw new IllegalArgumentException("Digits < 0");
204 // the other parameters cannot be invalid if we got here
205 precision = setPrecision;
206 }
207
208 /**
209 * Returns the {@code precision} setting.
210 * This value is always non-negative.
211 *
212 * @return an {@code int} which is the value of the {@code precision}
213 * setting
214 */
215 public int getPrecision() {
216 return precision;
217 }
218
219 /**
220 * Returns the roundingMode setting.
221 * This will be one of
222 * {@link RoundingMode#CEILING},
223 * {@link RoundingMode#DOWN},
224 * {@link RoundingMode#FLOOR},
225 * {@link RoundingMode#HALF_DOWN},
226 * {@link RoundingMode#HALF_EVEN},
227 * {@link RoundingMode#HALF_UP},
228 * {@link RoundingMode#UNNECESSARY}, or
229 * {@link RoundingMode#UP}.
230 *
231 * @return a {@code RoundingMode} object which is the value of the
232 * {@code roundingMode} setting
233 */
234
235 public RoundingMode getRoundingMode() {
236 return roundingMode;
237 }
238
239 /**
240 * Compares this {@code MathContext} with the specified
241 * {@code Object} for equality.
242 *
243 * @param x {@code Object} to which this {@code MathContext} is to
244 * be compared.
245 * @return {@code true} if and only if the specified {@code Object} is
246 * a {@code MathContext} object which has exactly the same
247 * settings as this object
248 */
249 public boolean equals(Object x){
250 MathContext mc;
251 if (!(x instanceof MathContext))
252 return false;
253 mc = (MathContext) x;
254 return mc.precision == this.precision
255 && mc.roundingMode == this.roundingMode; // no need for .equals()
256 }
257
258 /**
259 * Returns the hash code for this {@code MathContext}.
260 *
261 * @return hash code for this {@code MathContext}
262 */
263 public int hashCode() {
264 return this.precision + roundingMode.hashCode() * 59;
265 }
266
267 /**
268 * Returns the string representation of this {@code MathContext}.
269 * The {@code String} returned represents the settings of the
270 * {@code MathContext} object as two space-delimited words
271 * (separated by a single space character, <code>'\u0020'</code>,
272 * and with no leading or trailing white space), as follows:
273 * <ol>
274 * <li>
275 * The string {@code "precision="}, immediately followed
276 * by the value of the precision setting as a numeric string as if
277 * generated by the {@link Integer#toString(int) Integer.toString}
278 * method.
279 *
280 * <li>
281 * The string {@code "roundingMode="}, immediately
282 * followed by the value of the {@code roundingMode} setting as a
283 * word. This word will be the same as the name of the
284 * corresponding public constant in the {@link RoundingMode}
285 * enum.
286 * </ol>
287 * <p>
288 * For example:
289 * <pre>
290 * precision=9 roundingMode=HALF_UP
291 * </pre>
292 *
293 * Additional words may be appended to the result of
294 * {@code toString} in the future if more properties are added to
295 * this class.
296 *
297 * @return a {@code String} representing the context settings
298 */
299 public java.lang.String toString() {
300 return "precision=" + precision + " " +
301 "roundingMode=" + roundingMode.toString();
302 }
303
304 // Private methods
305
306 /**
307 * Reconstitute the {@code MathContext} instance from a stream (that is,
308 * deserialize it).
309 *
310 * @param s the stream being read.
311 */
312 private void readObject(java.io.ObjectInputStream s)
313 throws java.io.IOException, ClassNotFoundException {
314 s.defaultReadObject(); // read in all fields
315 // validate possibly bad fields
316 if (precision < MIN_DIGITS) {
317 String message = "MathContext: invalid digits in stream";
318 throw new java.io.StreamCorruptedException(message);
319 }
320 if (roundingMode == null) {
321 String message = "MathContext: null roundingMode in stream";
322 throw new java.io.StreamCorruptedException(message);
323 }
324 }
325
326 }