精确计算时，经常会涉及到“保留位数”或“数值舍入”的情况。
“保留位数”说白了就是“数值舍入”。舍入的关键就是规定好舍入时对保留位数如何进位。RoundingMode就提供了舍入的8种进位规则。
说再多也比不上源码！直接上JDK8的源码。而且源码里有注释有解说还有示例，清晰明了。
/* * %W% %E% * * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ /* * @(#)RoundingMode.java 1.x 01/xx/xx * * Copyright (c) 2001, Oracle and/or its affiliates. All rights reserved. * Portions Copyright IBM Corporation, 2001. All Rights Reserved. * * This software is the proprietary information of Oracle. * Use is subject to license terms. * */ package java.math; /** * Specifies a <i>rounding behavior</i> for numerical operations * capable of discarding precision. Each rounding mode indicates how * the least significant returned digit of a rounded result is to be * calculated. If fewer digits are returned than the digits needed to * represent the exact numerical result, the discarded digits will be * referred to as the <i>discarded fraction</i> regardless the digits' * contribution to the value of the number. In other words, * considered as a numerical value, the discarded fraction could have * an absolute value greater than one. * * <p>Each rounding mode description includes a table listing how * different two-digit decimal values would round to a one digit * decimal value under the rounding mode in question. The result * column in the tables could be gotten by creating a * <tt>BigDecimal</tt> number with the specified value, forming a * {@link MathContext} object with the proper settings * (<tt>precision</tt> set to <tt>1</tt>, and the * <tt>roundingMode</tt> set to the rounding mode in question), and * calling {@link BigDecimal#round round} on this number with the * proper <tt>MathContext</tt>. A summary table showing the results * of these rounding operations for all rounding modes appears below. * *<p> *<table border> * <caption top><h3>Summary of Rounding Operations Under Different Rounding Modes</h3></caption> * <tr><th></th><th colspan=8>Result of rounding input to one digit with the given * rounding mode</th> * <tr valign=top> * <th>Input Number</th> <th><tt>UP</tt></th> * <th><tt>DOWN</tt></th> * <th><tt>CEILING</tt></th> * <th><tt>FLOOR</tt></th> * <th><tt>HALF_UP</tt></th> * <th><tt>HALF_DOWN</tt></th> * <th><tt>HALF_EVEN</tt></th> * <th><tt>UNNECESSARY</tt></th> * * <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> * <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> * <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> * <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> * <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> * <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> * <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> * <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> * <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> * <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> *</table> * * * <p>This <tt>enum</tt> is intended to replace the integer-based * enumeration of rounding mode constants in {@link BigDecimal} * ({@link BigDecimal#ROUND_UP}, {@link BigDecimal#ROUND_DOWN}, * etc. ). * * @see BigDecimal * @see MathContext * @version 1.x 01/xx/xx * @author Josh Bloch * @author Mike Cowlishaw * @author Joseph D. Darcy * @since 1.5 */ public enum RoundingMode { /** * Rounding mode to round away from zero. Always increments the * digit prior to a non-zero discarded fraction. Note that this * rounding mode never decreases the magnitude of the calculated * value. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>UP</tt> rounding *<tr align=right><td>5.5</td> <td>6</td> *<tr align=right><td>2.5</td> <td>3</td> *<tr align=right><td>1.6</td> <td>2</td> *<tr align=right><td>1.1</td> <td>2</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-2</td> *<tr align=right><td>-1.6</td> <td>-2</td> *<tr align=right><td>-2.5</td> <td>-3</td> *<tr align=right><td>-5.5</td> <td>-6</td> *</table> */ UP(BigDecimal.ROUND_UP), /** * Rounding mode to round towards zero. Never increments the digit * prior to a discarded fraction (i.e., truncates). Note that this * rounding mode never increases the magnitude of the calculated value. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>DOWN</tt> rounding *<tr align=right><td>5.5</td> <td>5</td> *<tr align=right><td>2.5</td> <td>2</td> *<tr align=right><td>1.6</td> <td>1</td> *<tr align=right><td>1.1</td> <td>1</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-1</td> *<tr align=right><td>-1.6</td> <td>-1</td> *<tr align=right><td>-2.5</td> <td>-2</td> *<tr align=right><td>-5.5</td> <td>-5</td> *</table> */ DOWN(BigDecimal.ROUND_DOWN), /** * Rounding mode to round towards positive infinity. If the * result is positive, behaves as for <tt>RoundingMode.UP</tt>; * if negative, behaves as for <tt>RoundingMode.DOWN</tt>. Note * that this rounding mode never decreases the calculated value. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>CEILING</tt> rounding *<tr align=right><td>5.5</td> <td>6</td> *<tr align=right><td>2.5</td> <td>3</td> *<tr align=right><td>1.6</td> <td>2</td> *<tr align=right><td>1.1</td> <td>2</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-1</td> *<tr align=right><td>-1.6</td> <td>-1</td> *<tr align=right><td>-2.5</td> <td>-2</td> *<tr align=right><td>-5.5</td> <td>-5</td> *</table> */ CEILING(BigDecimal.ROUND_CEILING), /** * Rounding mode to round towards negative infinity. If the * result is positive, behave as for <tt>RoundingMode.DOWN</tt>; * if negative, behave as for <tt>RoundingMode.UP</tt>. Note that * this rounding mode never increases the calculated value. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>FLOOR</tt> rounding *<tr align=right><td>5.5</td> <td>5</td> *<tr align=right><td>2.5</td> <td>2</td> *<tr align=right><td>1.6</td> <td>1</td> *<tr align=right><td>1.1</td> <td>1</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-2</td> *<tr align=right><td>-1.6</td> <td>-2</td> *<tr align=right><td>-2.5</td> <td>-3</td> *<tr align=right><td>-5.5</td> <td>-6</td> *</table> */ FLOOR(BigDecimal.ROUND_FLOOR), /** * Rounding mode to round towards "nearest neighbor" * unless both neighbors are equidistant, in which case round up. * Behaves as for <tt>RoundingMode.UP</tt> if the discarded * fraction is >= 0.5; otherwise, behaves as for * <tt>RoundingMode.DOWN</tt>. Note that this is the rounding * mode commonly taught at school. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>HALF_UP</tt> rounding *<tr align=right><td>5.5</td> <td>6</td> *<tr align=right><td>2.5</td> <td>3</td> *<tr align=right><td>1.6</td> <td>2</td> *<tr align=right><td>1.1</td> <td>1</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-1</td> *<tr align=right><td>-1.6</td> <td>-2</td> *<tr align=right><td>-2.5</td> <td>-3</td> *<tr align=right><td>-5.5</td> <td>-6</td> *</table> */ HALF_UP(BigDecimal.ROUND_HALF_UP), /** * Rounding mode to round towards "nearest neighbor" * unless both neighbors are equidistant, in which case round * down. Behaves as for <tt>RoundingMode.UP</tt> if the discarded * fraction is > 0.5; otherwise, behaves as for * <tt>RoundingMode.DOWN</tt>. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>HALF_DOWN</tt> rounding *<tr align=right><td>5.5</td> <td>5</td> *<tr align=right><td>2.5</td> <td>2</td> *<tr align=right><td>1.6</td> <td>2</td> *<tr align=right><td>1.1</td> <td>1</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-1</td> *<tr align=right><td>-1.6</td> <td>-2</td> *<tr align=right><td>-2.5</td> <td>-2</td> *<tr align=right><td>-5.5</td> <td>-5</td> *</table> */ HALF_DOWN(BigDecimal.ROUND_HALF_DOWN), /** * Rounding mode to round towards the "nearest neighbor" * unless both neighbors are equidistant, in which case, round * towards the even neighbor. Behaves as for * <tt>RoundingMode.HALF_UP</tt> if the digit to the left of the * discarded fraction is odd; behaves as for * <tt>RoundingMode.HALF_DOWN</tt> if it's even. Note that this * is the rounding mode that statistically minimizes cumulative * error when applied repeatedly over a sequence of calculations. * It is sometimes known as "Banker's rounding," and is * chiefly used in the USA. This rounding mode is analogous to * the rounding policy used for <tt>float</tt> and <tt>double</tt> * arithmetic in Java. * *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>HALF_EVEN</tt> rounding *<tr align=right><td>5.5</td> <td>6</td> *<tr align=right><td>2.5</td> <td>2</td> *<tr align=right><td>1.6</td> <td>2</td> *<tr align=right><td>1.1</td> <td>1</td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>-1</td> *<tr align=right><td>-1.6</td> <td>-2</td> *<tr align=right><td>-2.5</td> <td>-2</td> *<tr align=right><td>-5.5</td> <td>-6</td> *</table> */ HALF_EVEN(BigDecimal.ROUND_HALF_EVEN), /** * Rounding mode to assert that the requested operation has an exact * result, hence no rounding is necessary. If this rounding mode is * specified on an operation that yields an inexact result, an * <tt>ArithmeticException</tt> is thrown. *<p>Example: *<table border> *<tr valign=top><th>Input Number</th> * <th>Input rounded to one digit<br> with <tt>UNNECESSARY</tt> rounding *<tr align=right><td>5.5</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>2.5</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>1.6</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>1.1</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>1.0</td> <td>1</td> *<tr align=right><td>-1.0</td> <td>-1</td> *<tr align=right><td>-1.1</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>-1.6</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>-2.5</td> <td>throw <tt>ArithmeticException</tt></td> *<tr align=right><td>-5.5</td> <td>throw <tt>ArithmeticException</tt></td> *</table> */ UNNECESSARY(BigDecimal.ROUND_UNNECESSARY); // Corresponding BigDecimal rounding constant final int oldMode; /** * Constructor * * @param oldMode The <tt>BigDecimal</tt> constant corresponding to * this mode */ private RoundingMode(int oldMode) { this.oldMode = oldMode; } /** * Returns the <tt>RoundingMode</tt> object corresponding to a * legacy integer rounding mode constant in {@link BigDecimal}. * * @param rm legacy integer rounding mode to convert * @return <tt>RoundingMode</tt> corresponding to the given integer. * @throws IllegalArgumentException integer is out of range */ public static RoundingMode valueOf(int rm) { switch(rm) { case BigDecimal.ROUND_UP: return UP; case BigDecimal.ROUND_DOWN: return DOWN; case BigDecimal.ROUND_CEILING: return CEILING; case BigDecimal.ROUND_FLOOR: return FLOOR; case BigDecimal.ROUND_HALF_UP: return HALF_UP; case BigDecimal.ROUND_HALF_DOWN: return HALF_DOWN; case BigDecimal.ROUND_HALF_EVEN: return HALF_EVEN; case BigDecimal.ROUND_UNNECESSARY: return UNNECESSARY; default: throw new IllegalArgumentException("argument out of range"); } } }看完了源码，我理解后总结出来的记忆秘籍是：（关键字“都要”）。
下面的例子，都是舍去小数位，只保留到个位数。舍去小数位时对保留的个位数如何进位，RoundingMode提供的8种规则如下：
1.UP：不管是正数还是负数，按其在Y轴上的位置，如有被舍位数都要取其趋于U两端±∞的值；
如1.1~1.9的趋于＋∞的值是2，-1.9~-1.1的趋于－∞的值是-2；
2.DOWN：不管是正数还是负数，按其在Y轴上的位置，如有被舍位数都要取其趋于0的值；
如1.1~1.9的趋于0的值是1，-1.9~-1.1趋于0的值是-1；
3.CEILING：不管是正数还是负数，按其在Y轴上的位置，如有被舍位数都要取其CEILING天花板值；
如1.1~1.9的CEILING天花板值是2，-1.9~-1.1的CEILING天花板值是-1；
4.FLOOR：不管是正数还是负数，按其在Y轴上的位置，如有被舍位数都要取其FLOOR地板值；
如1.1~1.9的FLOOR地板值是1，-1.9~-1.1的FLOOR地板值是-2；
理解识记以上4个就很好办了，另外4个是衍生出来的：
5.HALF_UP：不管是正数还是负数，按其在Y轴上的位置，被舍位数如果up than half达半(即0.5~0.9)都要取其趋于U两端±∞的值（潜台词：反之则取其趋于0的值），即五入四舍；
如1.5和-1.5达半要取趋于±∞的值2和-2，1.4和-1.4未达半只能取趋于0的值1和-1；
6.HALF_DOWN：不管是正数还是负数，按其在Y轴上的位置，被舍位数如果down than half未过半(即0.1~0.5)都要取其趋于0的值（潜台词：反之则取其趋于U两端±∞的值），即五舍六入；
如1.5和-1.5未过半要取趋于0的值1和-1，1.6和-1.6过半只能取趋于±∞的值2和-2；
7.HALF_EVEN：不管是正数还是负数，按其在Y轴上的位置，如有被舍位数都要取其趋于EVEN公平的值（潜台词：向谁靠拢就取谁，但0.5正居中间要根据保留位数的奇偶来奇up偶down）；
如1.4和-1.4向1和-1靠拢；1.6和-1.6向2和-2靠拢；
如1.5和-1.5保留的个位数是奇数1则up取趋于±∞的值2和-2，2.5和-2.5保留的个位数是偶数2则down取趋于0的值2和-2；
8.UNNECESSARY：不需要做数值的舍入；经常在除法时抛错，除不尽时会抛出ArithmeticException。
/* * Copyright (c) 2003, 2007, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ /* * Portions Copyright IBM Corporation, 1997, 2001. All Rights Reserved. */ package java.math; import java.io.*; /** * Immutable objects which encapsulate the context settings which * describe certain rules for numerical operators, such as those * implemented by the {@link BigDecimal} class. * * <p>The base-independent settings are: * <ol> * <li>{@code precision}: * the number of digits to be used for an operation; results are * rounded to this precision * * <li>{@code roundingMode}: * a {@link RoundingMode} object which specifies the algorithm to be * used for rounding. * </ol> * * @see BigDecimal * @see RoundingMode * @author Mike Cowlishaw * @author Joseph D. Darcy * @since 1.5 */ public final class MathContext implements Serializable { /* ----- Constants ----- */ // defaults for constructors private static final int DEFAULT_DIGITS = 9; private static final RoundingMode DEFAULT_ROUNDINGMODE = RoundingMode.HALF_UP; // Smallest values for digits (Maximum is Integer.MAX_VALUE) private static final int MIN_DIGITS = 0; // Serialization version private static final long serialVersionUID = 5579720004786848255L; /* ----- Public Properties ----- */ /** * A {@code MathContext} object whose settings have the values * required for unlimited precision arithmetic. * The values of the settings are: * <code> * precision=0 roundingMode=HALF_UP * </code> */ public static final MathContext UNLIMITED = new MathContext(0, RoundingMode.HALF_UP); /** * A {@code MathContext} object with a precision setting * matching the IEEE 754R Decimal32 format, 7 digits, and a * rounding mode of {@link RoundingMode#HALF_EVEN HALF_EVEN}, the * IEEE 754R default. */ public static final MathContext DECIMAL32 = new MathContext(7, RoundingMode.HALF_EVEN); /** * A {@code MathContext} object with a precision setting * matching the IEEE 754R Decimal64 format, 16 digits, and a * rounding mode of {@link RoundingMode#HALF_EVEN HALF_EVEN}, the * IEEE 754R default. */ public static final MathContext DECIMAL64 = new MathContext(16, RoundingMode.HALF_EVEN); /** * A {@code MathContext} object with a precision setting * matching the IEEE 754R Decimal128 format, 34 digits, and a * rounding mode of {@link RoundingMode#HALF_EVEN HALF_EVEN}, the * IEEE 754R default. */ public static final MathContext DECIMAL128 = new MathContext(34, RoundingMode.HALF_EVEN); /* ----- Shared Properties ----- */ /** * The number of digits to be used for an operation. A value of 0 * indicates that unlimited precision (as many digits as are * required) will be used. Note that leading zeros (in the * coefficient of a number) are never significant. * * <p>{@code precision} will always be non-negative. * * @serial */ final int precision; /** * The rounding algorithm to be used for an operation. * * @see RoundingMode * @serial */ final RoundingMode roundingMode; /* ----- Constructors ----- */ /** * Constructs a new {@code MathContext} with the specified * precision and the {@link RoundingMode#HALF_UP HALF_UP} rounding * mode. * * @param setPrecision The non-negative {@code int} precision setting. * @throws IllegalArgumentException if the {@code setPrecision} parameter is less * than zero. */ public MathContext(int setPrecision) { this(setPrecision, DEFAULT_ROUNDINGMODE); return; } /** * Constructs a new {@code MathContext} with a specified * precision and rounding mode. * * @param setPrecision The non-negative {@code int} precision setting. * @param setRoundingMode The rounding mode to use. * @throws IllegalArgumentException if the {@code setPrecision} parameter is less * than zero. * @throws NullPointerException if the rounding mode argument is {@code null} */ public MathContext(int setPrecision, RoundingMode setRoundingMode) { if (setPrecision < MIN_DIGITS) throw new IllegalArgumentException("Digits < 0"); if (setRoundingMode == null) throw new NullPointerException("null RoundingMode"); precision = setPrecision; roundingMode = setRoundingMode; return; } /** * Constructs a new {@code MathContext} from a string. * * The string must be in the same format as that produced by the * {@link #toString} method. * * <p>An {@code IllegalArgumentException} is thrown if the precision * section of the string is out of range ({@code < 0}) or the string is * not in the format created by the {@link #toString} method. * * @param val The string to be parsed * @throws IllegalArgumentException if the precision section is out of range * or of incorrect format * @throws NullPointerException if the argument is {@code null} */ public MathContext(String val) { boolean bad = false; int setPrecision; if (val == null) throw new NullPointerException("null String"); try { // any error here is a string format problem if (!val.startsWith("precision=")) throw new RuntimeException(); int fence = val.indexOf(' '); // could be -1 int off = 10; // where value starts setPrecision = Integer.parseInt(val.substring(10, fence)); if (!val.startsWith("roundingMode=", fence+1)) throw new RuntimeException(); off = fence + 1 + 13; String str = val.substring(off, val.length()); roundingMode = RoundingMode.valueOf(str); } catch (RuntimeException re) { throw new IllegalArgumentException("bad string format"); } if (setPrecision < MIN_DIGITS) throw new IllegalArgumentException("Digits < 0"); // the other parameters cannot be invalid if we got here precision = setPrecision; } /** * Returns the {@code precision} setting. * This value is always non-negative. * * @return an {@code int} which is the value of the {@code precision} * setting */ public int getPrecision() { return precision; } /** * Returns the roundingMode setting. * This will be one of * {@link RoundingMode#CEILING}, * {@link RoundingMode#DOWN}, * {@link RoundingMode#FLOOR}, * {@link RoundingMode#HALF_DOWN}, * {@link RoundingMode#HALF_EVEN}, * {@link RoundingMode#HALF_UP}, * {@link RoundingMode#UNNECESSARY}, or * {@link RoundingMode#UP}. * * @return a {@code RoundingMode} object which is the value of the * {@code roundingMode} setting */ public RoundingMode getRoundingMode() { return roundingMode; } /** * Compares this {@code MathContext} with the specified * {@code Object} for equality. * * @param x {@code Object} to which this {@code MathContext} is to * be compared. * @return {@code true} if and only if the specified {@code Object} is * a {@code MathContext} object which has exactly the same * settings as this object */ public boolean equals(Object x){ MathContext mc; if (!(x instanceof MathContext)) return false; mc = (MathContext) x; return mc.precision == this.precision && mc.roundingMode == this.roundingMode; // no need for .equals() } /** * Returns the hash code for this {@code MathContext}. * * @return hash code for this {@code MathContext} */ public int hashCode() { return this.precision + roundingMode.hashCode() * 59; } /** * Returns the string representation of this {@code MathContext}. * The {@code String} returned represents the settings of the * {@code MathContext} object as two space-delimited words * (separated by a single space character, <tt>'\u0020'</tt>, * and with no leading or trailing white space), as follows: * <ol> * <li> * The string {@code "precision="}, immediately followed * by the value of the precision setting as a numeric string as if * generated by the {@link Integer#toString(int) Integer.toString} * method. * * <li> * The string {@code "roundingMode="}, immediately * followed by the value of the {@code roundingMode} setting as a * word. This word will be the same as the name of the * corresponding public constant in the {@link RoundingMode} * enum. * </ol> * <p> * For example: * <pre> * precision=9 roundingMode=HALF_UP * </pre> * * Additional words may be appended to the result of * {@code toString} in the future if more properties are added to * this class. * * @return a {@code String} representing the context settings */ public java.lang.String toString() { return "precision=" + precision + " " + "roundingMode=" + roundingMode.toString(); } // Private methods /** * Reconstitute the {@code MathContext} instance from a stream (that is, * deserialize it). * * @param s the stream being read. */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { s.defaultReadObject(); // read in all fields // validate possibly bad fields if (precision < MIN_DIGITS) { String message = "MathContext: invalid digits in stream"; throw new java.io.StreamCorruptedException(message); } if (roundingMode == null) { String message = "MathContext: null roundingMode in stream"; throw new java.io.StreamCorruptedException(message); } } }