1. /*

  2.  * @(#)RoundingMode.java	1.3 04/06/18

  3.  *

  4.  * Copyright 2004 Sun Microsystems, Inc. All rights reserved.

  5.  * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.

  6.  */

  7. 

  8. /*

  9.  * @(#)RoundingMode.java  1.x 01/xx/xx

  10.  *

  11.  * Copyright 2001 Sun Microsystems, Inc. All Rights Reserved.

  12.  * Portions Copyright IBM Corporation, 2001. All Rights Reserved.

  13.  *

  14.  * This software is the proprietary information of Sun Microsystems, Inc.

  15.  * Use is subject to license terms.

  16.  *

  17.  */

  18. package java.math;

  19. 

  20. /**

  21.  * Specifies a <i>rounding behavior</i> for numerical operations

  22.  * capable of discarding precision. Each rounding mode indicates how

  23.  * the least significant returned digit of a rounded result is to be

  24.  * calculated.  If fewer digits are returned than the digits needed to

  25.  * represent the exact numerical result, the discarded digits will be

  26.  * referred to as the <i>discarded fraction</i> regardless the digits'

  27.  * contribution to the value of the number.  In other words,

  28.  * considered as a numerical value, the discarded fraction could have

  29.  * an absolute value greater than one.

  30.  *

  31.  * <p>Each rounding mode description includes a table listing how

  32.  * different two-digit decimal values would round to a one digit

  33.  * decimal value under the rounding mode in question.  The result

  34.  * column in the tables could be gotten by creating a

  35.  * <tt>BigDecimal</tt> number with the specified value, forming a

  36.  * {@link MathContext} object with the proper settings

  37.  * (<tt>precision</tt> set to <tt>1</tt>, and the

  38.  * <tt>roundingMode</tt> set to the rounding mode in question), and

  39.  * calling {@link BigDecimal#round round} on this number with the

  40.  * proper <tt>MathContext</tt>.  A summary table showing the results

  41.  * of these rounding operations for all rounding modes appears below.

  42.  *

  43.  *<p>

  44.  *<table border>

  45.  * <caption top><h3>Summary of Rounding Operations Under Different Rounding Modes</h3></caption>

  46.  * <tr><th></th><th colspan=8>Result of rounding input to one digit with the given 

  47.  *                           rounding mode</th>

  48.  * <tr valign=top>

  49.  * <th>Input Number</th>	 <th><tt>UP</tt></th> 

  50.  *                                           <th><tt>DOWN</tt></th> 

  51.  *                                                        <th><tt>CEILING</tt></th>

  52.  *                                                                       <th><tt>FLOOR</tt></th>

  53.  *                                                                                    <th><tt>HALF_UP</tt></th>

  54.  *                                                                                                   <th><tt>HALF_DOWN</tt></th>

  55.  *                                                                                                                    <th><tt>HALF_EVEN</tt></th>

  56.  *                                                                                                                                     <th><tt>UNNECESSARY</tt></th>

  57.  *    

  58.  * <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 <tt>ArithmeticException</tt></td>

  59.  * <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 <tt>ArithmeticException</tt></td>

  60.  * <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 <tt>ArithmeticException</tt></td>

  61.  * <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 <tt>ArithmeticException</tt></td>

  62.  * <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>                                

  63.  * <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>                               

  64.  * <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 <tt>ArithmeticException</tt></td>

  65.  * <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 <tt>ArithmeticException</tt></td>

  66.  * <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 <tt>ArithmeticException</tt></td>

  67.  * <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 <tt>ArithmeticException</tt></td>

  68.  *</table>

  69.  *

  70.  * 

  71.  * <p>This <tt>enum</tt> is intended to replace the integer-based

  72.  * enumeration of rounding mode constants in {@link BigDecimal}

  73.  * ({@link BigDecimal#ROUND_UP}, {@link BigDecimal#ROUND_DOWN},

  74.  * etc. ).

  75.  *

  76.  * @see     BigDecimal

  77.  * @see     MathContext

  78.  * @version 1.x 01/xx/xx

  79.  * @author  Josh Bloch

  80.  * @author  Mike Cowlishaw

  81.  * @author  Joseph D. Darcy

  82.  */

  83. public enum RoundingMode {

  84. 

  85. 	/**

  86. 	 * Rounding mode to round away from zero.  Always increments the

  87. 	 * digit prior to a non-zero discarded fraction.  Note that this

  88. 	 * rounding mode never decreases the magnitude of the calculated

  89. 	 * value.

  90. 	 *

  91. 	 *<p>Example:

  92. 	 *<table border>

  93. 	 *<tr valign=top><th>Input Number</th>

  94. 	 *    <th>Input rounded to one digit<br> with <tt>UP</tt> rounding

  95. 	 *<tr align=right><td>5.5</td>	<td>6</td>

  96. 	 *<tr align=right><td>2.5</td>	<td>3</td>

  97. 	 *<tr align=right><td>1.6</td>	<td>2</td>

  98. 	 *<tr align=right><td>1.1</td>	<td>2</td>

  99. 	 *<tr align=right><td>1.0</td>	<td>1</td>

  100. 	 *<tr align=right><td>-1.0</td>	<td>-1</td>

  101. 	 *<tr align=right><td>-1.1</td>	<td>-2</td>

  102. 	 *<tr align=right><td>-1.6</td>	<td>-2</td>

  103. 	 *<tr align=right><td>-2.5</td>	<td>-3</td>

  104. 	 *<tr align=right><td>-5.5</td>	<td>-6</td>

  105. 	 *</table>

  106. 	 */

  107.     UP(BigDecimal.ROUND_UP),

  108. 	    

  109. 	/**

  110. 	 * Rounding mode to round towards zero.  Never increments the digit

  111. 	 * prior to a discarded fraction (i.e., truncates).  Note that this

  112. 	 * rounding mode never increases the magnitude of the calculated value.

  113. 	 *

  114. 	 *<p>Example:

  115. 	 *<table border>

  116. 	 *<tr valign=top><th>Input Number</th>

  117. 	 *    <th>Input rounded to one digit<br> with <tt>DOWN</tt> rounding

  118. 	 *<tr align=right><td>5.5</td>	<td>5</td>

  119. 	 *<tr align=right><td>2.5</td>	<td>2</td>

  120. 	 *<tr align=right><td>1.6</td>	<td>1</td>

  121. 	 *<tr align=right><td>1.1</td>	<td>1</td>

  122. 	 *<tr align=right><td>1.0</td>	<td>1</td>

  123. 	 *<tr align=right><td>-1.0</td>	<td>-1</td>

  124. 	 *<tr align=right><td>-1.1</td>	<td>-1</td>

  125. 	 *<tr align=right><td>-1.6</td>	<td>-1</td>

  126. 	 *<tr align=right><td>-2.5</td>	<td>-2</td>

  127. 	 *<tr align=right><td>-5.5</td>	<td>-5</td>

  128. 	 *</table>

  129. 	 */

  130.     DOWN(BigDecimal.ROUND_DOWN),

  131. 	    

  132. 	/**

  133. 	 * Rounding mode to round towards positive infinity.  If the

  134. 	 * result is positive, behaves as for <tt>RoundingMode.UP</tt>

  135. 	 * if negative, behaves as for <tt>RoundingMode.DOWN</tt>.  Note

  136. 	 * that this rounding mode never decreases the calculated value.

  137. 	 *

  138. 	 *<p>Example:

  139. 	 *<table border>

  140. 	 *<tr valign=top><th>Input Number</th>

  141. 	 *    <th>Input rounded to one digit<br> with <tt>CEILING</tt> rounding

  142. 	 *<tr align=right><td>5.5</td>	<td>6</td>

  143. 	 *<tr align=right><td>2.5</td>	<td>3</td>

  144. 	 *<tr align=right><td>1.6</td>	<td>2</td>

  145. 	 *<tr align=right><td>1.1</td>	<td>2</td>

  146. 	 *<tr align=right><td>1.0</td>	<td>1</td>

  147. 	 *<tr align=right><td>-1.0</td>	<td>-1</td>

  148. 	 *<tr align=right><td>-1.1</td>	<td>-1</td>

  149. 	 *<tr align=right><td>-1.6</td>	<td>-1</td>

  150. 	 *<tr align=right><td>-2.5</td>	<td>-2</td>

  151. 	 *<tr align=right><td>-5.5</td>	<td>-5</td>

  152. 	 *</table>

  153. 	 */

  154.     CEILING(BigDecimal.ROUND_CEILING),

  155. 

  156. 	/**

  157. 	 * Rounding mode to round towards negative infinity.  If the

  158. 	 * result is positive, behave as for <tt>RoundingMode.DOWN</tt>

  159. 	 * if negative, behave as for <tt>RoundingMode.UP</tt>.  Note that

  160. 	 * this rounding mode never increases the calculated value.

  161. 	 *

  162. 	 *<p>Example:

  163. 	 *<table border>

  164. 	 *<tr valign=top><th>Input Number</th>

  165. 	 *    <th>Input rounded to one digit<br> with <tt>FLOOR</tt> rounding

  166. 	 *<tr align=right><td>5.5</td>	<td>5</td>

  167. 	 *<tr align=right><td>2.5</td>	<td>2</td>

  168. 	 *<tr align=right><td>1.6</td>	<td>1</td>

  169. 	 *<tr align=right><td>1.1</td>	<td>1</td>

  170. 	 *<tr align=right><td>1.0</td>	<td>1</td>

  171. 	 *<tr align=right><td>-1.0</td>	<td>-1</td>

  172. 	 *<tr align=right><td>-1.1</td>	<td>-2</td>

  173. 	 *<tr align=right><td>-1.6</td>	<td>-2</td>

  174. 	 *<tr align=right><td>-2.5</td>	<td>-3</td>

  175. 	 *<tr align=right><td>-5.5</td>	<td>-6</td>

  176. 	 *</table>

  177. 	 */

  178.     FLOOR(BigDecimal.ROUND_FLOOR),

  179. 

  180. 	/**

  181. 	 * Rounding mode to round towards "nearest neighbor"

  182. 	 * unless both neighbors are equidistant, in which case round up.

  183. 	 * Behaves as for <tt>RoundingMode.UP</tt> if the discarded

  184. 	 * fraction is >= 0.5; otherwise, behaves as for

  185. 	 * <tt>RoundingMode.DOWN</tt>.  Note that this is the rounding

  186. 	 * mode commonly taught at school.

  187. 	 *

  188. 	 *<p>Example:

  189. 	 *<table border>

  190. 	 *<tr valign=top><th>Input Number</th>

  191. 	 *    <th>Input rounded to one digit<br> with <tt>HALF_UP</tt> rounding

  192. 	 *<tr align=right><td>5.5</td>	<td>6</td>

  193. 	 *<tr align=right><td>2.5</td>	<td>3</td>

  194. 	 *<tr align=right><td>1.6</td>	<td>2</td>

  195. 	 *<tr align=right><td>1.1</td>	<td>1</td>

  196. 	 *<tr align=right><td>1.0</td>	<td>1</td>

  197. 	 *<tr align=right><td>-1.0</td>	<td>-1</td>

  198. 	 *<tr align=right><td>-1.1</td>	<td>-1</td>

  199. 	 *<tr align=right><td>-1.6</td>	<td>-2</td>

  200. 	 *<tr align=right><td>-2.5</td>	<td>-3</td>

  201. 	 *<tr align=right><td>-5.5</td>	<td>-6</td>

  202. 	 *</table>

  203. 	 */

  204.     HALF_UP(BigDecimal.ROUND_HALF_UP),

  205. 

  206. 	/**

  207. 	 * Rounding mode to round towards "nearest neighbor"

  208. 	 * unless both neighbors are equidistant, in which case round

  209. 	 * down.  Behaves as for <tt>RoundingMode.UP</tt> if the discarded

  210. 	 * fraction is > 0.5; otherwise, behaves as for

  211. 	 * <tt>RoundingMode.DOWN</tt>.

  212. 	 *

  213. 	 *<p>Example:

  214. 	 *<table border>

  215. 	 *<tr valign=top><th>Input Number</th>

  216. 	 *    <th>Input rounded to one digit<br> with <tt>HALF_DOWN</tt> rounding

  217. 	 *<tr align=right><td>5.5</td>	<td>5</td>

  218. 	 *<tr align=right><td>2.5</td>	<td>2</td>

  219. 	 *<tr align=right><td>1.6</td>	<td>2</td>

  220. 	 *<tr align=right><td>1.1</td>	<td>1</td>

  221. 	 *<tr align=right><td>1.0</td>	<td>1</td>

  222. 	 *<tr align=right><td>-1.0</td>	<td>-1</td>

  223. 	 *<tr align=right><td>-1.1</td>	<td>-1</td>

  224. 	 *<tr align=right><td>-1.6</td>	<td>-2</td>

  225. 	 *<tr align=right><td>-2.5</td>	<td>-2</td>

  226. 	 *<tr align=right><td>-5.5</td>	<td>-5</td>

  227. 	 *</table>

  228. 	 */

  229.     HALF_DOWN(BigDecimal.ROUND_HALF_DOWN),

  230. 

  231. 	/**

  232. 	 * Rounding mode to round towards the "nearest neighbor"

  233. 	 * unless both neighbors are equidistant, in which case, round

  234. 	 * towards the even neighbor.  Behaves as for

  235. 	 * <tt>RoundingMode.HALF_UP</tt> if the digit to the left of the

  236. 	 * discarded fraction is odd; behaves as for

  237. 	 * <tt>RoundingMode.HALF_DOWN</tt> if it's even.  Note that this

  238. 	 * is the rounding mode that statistically minimizes cumulative

  239. 	 * error when applied repeatedly over a sequence of calculations.

  240. 	 * It is sometimes known as "Banker's rounding," and is

  241. 	 * chiefly used in the USA.  This rounding mode is analogous to

  242. 	 * the rounding policy used for <tt>float</tt> and <tt>double</tt>

  243. 	 * arithmetic in Java.

  244. 	 *

  245. 	 *<p>Example:

  246. 	 *<table border>

  247. 	 *<tr valign=top><th>Input Number</th>

  248. 	 *    <th>Input rounded to one digit<br> with <tt>HALF_EVEN</tt> rounding

  249. 	 *<tr align=right><td>5.5</td>	<td>6</td>

  250. 	 *<tr align=right><td>2.5</td>	<td>2</td>

  251. 	 *<tr align=right><td>1.6</td>	<td>2</td>

  252. 	 *<tr align=right><td>1.1</td>	<td>1</td>

  253. 	 *<tr align=right><td>1.0</td>	<td>1</td>

  254. 	 *<tr align=right><td>-1.0</td>	<td>-1</td>

  255. 	 *<tr align=right><td>-1.1</td>	<td>-1</td>

  256. 	 *<tr align=right><td>-1.6</td>	<td>-2</td>

  257. 	 *<tr align=right><td>-2.5</td>	<td>-2</td>

  258. 	 *<tr align=right><td>-5.5</td>	<td>-6</td>

  259. 	 *</table>

  260. 	 */

  261.     HALF_EVEN(BigDecimal.ROUND_HALF_EVEN),

  262. 

  263. 	/**

  264. 	 * Rounding mode to assert that the requested operation has an exact

  265. 	 * result, hence no rounding is necessary.  If this rounding mode is

  266. 	 * specified on an operation that yields an inexact result, an

  267. 	 * <tt>ArithmeticException</tt> is thrown.

  268. 	 *<p>Example:

  269. 	 *<table border>

  270. 	 *<tr valign=top><th>Input Number</th>

  271. 	 *    <th>Input rounded to one digit<br> with <tt>UNNECESSARY</tt> rounding

  272. 	 *<tr align=right><td>5.5</td>	<td>throw <tt>ArithmeticException</tt></td>

  273. 	 *<tr align=right><td>2.5</td>	<td>throw <tt>ArithmeticException</tt></td>

  274. 	 *<tr align=right><td>1.6</td>	<td>throw <tt>ArithmeticException</tt></td>

  275. 	 *<tr align=right><td>1.1</td>	<td>throw <tt>ArithmeticException</tt></td>

  276. 	 *<tr align=right><td>1.0</td>	<td>1</td>

  277. 	 *<tr align=right><td>-1.0</td>	<td>-1</td>

  278. 	 *<tr align=right><td>-1.1</td>	<td>throw <tt>ArithmeticException</tt></td>

  279. 	 *<tr align=right><td>-1.6</td>	<td>throw <tt>ArithmeticException</tt></td>

  280. 	 *<tr align=right><td>-2.5</td>	<td>throw <tt>ArithmeticException</tt></td>

  281. 	 *<tr align=right><td>-5.5</td>	<td>throw <tt>ArithmeticException</tt></td>	

  282. 	 *</table>

  283. 	 */

  284.     UNNECESSARY(BigDecimal.ROUND_UNNECESSARY);

  285. 

  286.     // Corresponding BigDecimal rounding constant

  287.     final int oldMode;

  288. 

  289.     /**

  290.      * Constructor

  291.      *

  292.      * @param oldMode The <tt>BigDecimal</tt> constant corresponding to 

  293.      *        this mode

  294.      */

  295.     private RoundingMode(int oldMode) {

  296.         this.oldMode = oldMode;

  297.     }

  298. 

  299.     /**

  300.      * Returns the <tt>RoundingMode</tt> object corresponding to a

  301.      * legacy integer rounding mode constant in {@link BigDecimal}.

  302.      *

  303.      * @param  rm legacy integer rounding mode to convert

  304.      * @return <tt>RoundingMode</tt> corresponding to the given integer.

  305.      * @throws IllegalArgumentException integer is out of range

  306.      */

  307.     public static RoundingMode valueOf(int rm) {

  308. 	switch(rm) {

  309. 

  310. 	case BigDecimal.ROUND_UP:

  311. 	    return UP;

  312. 

  313. 	case BigDecimal.ROUND_DOWN:

  314. 	    return DOWN;

  315. 

  316. 	case BigDecimal.ROUND_CEILING:

  317. 	    return CEILING;

  318. 	    

  319. 	case BigDecimal.ROUND_FLOOR:

  320. 	    return FLOOR;

  321. 

  322. 	case BigDecimal.ROUND_HALF_UP:

  323. 	    return HALF_UP;

  324. 	    

  325. 	case BigDecimal.ROUND_HALF_DOWN:

  326. 	    return HALF_DOWN;

  327. 	    

  328. 	case BigDecimal.ROUND_HALF_EVEN:

  329. 	    return HALF_EVEN;

  330. 	    

  331. 	case BigDecimal.ROUND_UNNECESSARY:

  332. 	    return UNNECESSARY;

  333. 	    

  334. 	default:

  335. 	    throw new IllegalArgumentException("argument out of range");		

  336. 	}

  337.     }

  338. }