Non-terminating decimal expansion; no exact representable decimal result
翻译：无法终止小数点扩展; 没有确切的可表示的小数结果
出现的情形：
BigDecimal num1 = new BigDecimal("10");
BigDecimal num2 = new BigDecimal("3");
BigDecimal num3 = num1.divide(num2);
出现了无线循环小数。
可以使用devide重载方法BigDecimal.divide(BigDecimal divisor, int scale, RoundingMode roundingMode) ;
RoundingMode源码解析：
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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.
*
* 远离0的舍入模式。总是在非零的小数前增加数值。请注意，该舍入模式不会减小计算值的大小。
*
*<p>Example:
*<table border>
*<tr valign=top><th>Input Number</th>
* <th>Input rounded to one digit<br> with {@code UP} 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>
*
* 举个栗子：
* 输入一个数字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入后的数字：6 3 2 2 1 -1 -2 -2 -3 -6
*/
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.
*
* 靠近0的舍入模式。在放弃的小数之前不递增数值（即截断）。请注意，舍入模式不会增加计算值的大小。
*
*<p>Example:
*<table border>
*<tr valign=top><th>Input Number</th>
* <th>Input rounded to one digit<br> with {@code DOWN} 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>
*
* 举个栗子：
* 输入一个数字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入后的数字：5 2 1 1 1 -1 -1 -1 -2 -5
*/
DOWN(BigDecimal.ROUND_DOWN),
/**
* Rounding mode to round towards positive infinity. If the
* result is positive, behaves as for {@code RoundingMode.UP};
* if negative, behaves as for {@code RoundingMode.DOWN}. Note
* that this rounding mode never decreases the calculated value.
*
* 向正无穷大舍入。如果结果是正数，执行RoundingMode.UP；如果结果是负数，执行RoundingMode.DOWN。
* 请注意，这个舍入模式决不会减少计算值。
*
*<p>Example:
*<table border>
*<tr valign=top><th>Input Number</th>
* <th>Input rounded to one digit<br> with {@code CEILING} 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>
*
* 举个栗子：
* 输入一个数字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入后的数字：6 3 2 2 1 -1 -1 -1 -2 -5
*/
CEILING(BigDecimal.ROUND_CEILING),
/**
* Rounding mode to round towards negative infinity. If the
* result is positive, behave as for {@code RoundingMode.DOWN};
* if negative, behave as for {@code RoundingMode.UP}. Note that
* this rounding mode never increases the calculated value.
*
* 向负无穷大舍入。如果结果是正数，执行RoundingMode.DOWN；如果结果是负数，执行RoundingMode.UP。
*
*<p>Example:
*<table border>
*<tr valign=top><th>Input Number</th>
* <th>Input rounded to one digit<br> with {@code FLOOR} 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>
*
* 举个栗子：
* 输入一个数字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入后的数字：5 2 1 1 1 -1 -2 -2 -3 -6
*/
FLOOR(BigDecimal.ROUND_FLOOR),
/**
* Rounding mode to round towards {@literal "nearest neighbor"}
* unless both neighbors are equidistant, in which case round up.
* Behaves as for {@code RoundingMode.UP} if the discarded
* fraction is ≥ 0.5; otherwise, behaves as for
* {@code RoundingMode.DOWN}. Note that this is the rounding
* mode commonly taught at school.
*
* 向最邻近的地方舍入。除非离左右两边的的数值是等距的，那么就是用ROUND_UP模式。
* 如果舍弃的小数部分大于等于0.5，执行RoundingMode.UP，否则执行RoundingMode.DOWN。
* 请注意，这是学校常用的四舍五入舍入模式。
*
*<p>Example:
*<table border>
*<tr valign=top><th>Input Number</th>
* <th>Input rounded to one digit<br> with {@code HALF_UP} 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>
*
* 举个栗子：
* 输入一个数字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入后的数字：6 3 2 1 1 -1 -1 -2 -3 -6
*/
HALF_UP(BigDecimal.ROUND_HALF_UP),
/**
* Rounding mode to round towards {@literal "nearest neighbor"}
* unless both neighbors are equidistant, in which case round
* down. Behaves as for {@code RoundingMode.UP} if the discarded
* fraction is > 0.5; otherwise, behaves as for
* {@code RoundingMode.DOWN}.
*
* 向最邻近的地方舍入。除非离左右两边的的数值是等距的，那么就是用ROUND_DOWN模式。
* 如果舍弃的小数部分大于0.5，执行RoundingMode.UP，否则执行RoundingMode.DOWN。
*
*<p>Example:
*<table border>
*<tr valign=top><th>Input Number</th>
* <th>Input rounded to one digit<br> with {@code HALF_DOWN} 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>
*
* 举个栗子：
* 输入一个数字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入后的数字：5 2 2 1 1 -1 -1 -2 -2 -5
*/
HALF_DOWN(BigDecimal.ROUND_HALF_DOWN),
/**
* Rounding mode to round towards the {@literal "nearest neighbor"}
* unless both neighbors are equidistant, in which case, round
* towards the even neighbor. Behaves as for
* {@code RoundingMode.HALF_UP} if the digit to the left of the
* discarded fraction is odd; behaves as for
* {@code RoundingMode.HALF_DOWN} 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 {@literal "Banker's rounding,"} and is
* chiefly used in the USA. This rounding mode is analogous to
* the rounding policy used for {@code float} and {@code double}
* arithmetic in Java.
*
* 向最邻近的地方舍入。除非离左右两边的的数值是等距的，那么就向最邻近的偶数舍入。
* 如果舍弃部分左边的数字是奇数，执行RoundingMode.HALF_UP。如果是偶数，执行RoundingMode.HALF_DOWN。
* 请注意，这是一个舍入模式，当在一系列计算中重复应用时，可以统计学上最小化累积误差。
* 它有时被称为"银行家四舍五入"，主要用于美国。
* 这种舍入模式类似于Java中用于float和double算术的舍入策略。
*
*<p>Example:
*<table border>
*<tr valign=top><th>Input Number</th>
* <th>Input rounded to one digit<br> with {@code HALF_EVEN} 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>
*
* 举个栗子：
* 输入一个数字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入后的数字：6 2 2 1 1 -1 -1 -2 -2 -6
*/
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
* {@code ArithmeticException} is thrown.
*
* 舍入模式来断言所请求的操作具有确切的结果，因此不需要舍入。
* 如果在产生不精确结果的操作上指定了舍入模式，则抛出ArithmeticException。
*
*<p>Example:
*<table border>
*<tr valign=top><th>Input Number</th>
* <th>Input rounded to one digit<br> with {@code UNNECESSARY} rounding
*<tr align=right><td>5.5</td> <td>throw {@code ArithmeticException}</td>
*<tr align=right><td>2.5</td> <td>throw {@code ArithmeticException}</td>
*<tr align=right><td>1.6</td> <td>throw {@code ArithmeticException}</td>
*<tr align=right><td>1.1</td> <td>throw {@code ArithmeticException}</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 {@code ArithmeticException}</td>
*<tr align=right><td>-1.6</td> <td>throw {@code ArithmeticException}</td>
*<tr align=right><td>-2.5</td> <td>throw {@code ArithmeticException}</td>
*<tr align=right><td>-5.5</td> <td>throw {@code ArithmeticException}</td>
*</table>
*
* 举个栗子：
* 输入一个数字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入后的数字：异常 异常 异常 异常 1 -1 异常 异常 异常 异常
*/
UNNECESSARY(BigDecimal.ROUND_UNNECESSARY);
// Corresponding BigDecimal rounding constant
final int oldMode;
/**
* Constructor
*
* @param oldMode The {@code BigDecimal} constant corresponding to
* this mode
*/
private RoundingMode(int oldMode) {
this.oldMode = oldMode;
}
/**
* Returns the {@code RoundingMode} object corresponding to a
* legacy integer rounding mode constant in {@link BigDecimal}.
*
* 返回BigDecimal中对应于传统整数舍入模式常量的RoundingMode对象。
*
* @param rm legacy integer rounding mode to convert
* @return {@code RoundingMode} 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");
}
}
}