Non-terminating decimal expansion; no exact representable decimal result
翻譯：無法終止小數點擴展; 沒有確切的可表示的小數結果
出現的情形：
BigDecimal num1 = new BigDecimal("10");
BigDecimal num2 = new BigDecimal("3");
BigDecimal num3 = num1.divide(num2);
出現了無線循環小數。
可以使用devide重載方法BigDecimal.divide(BigDecimal divisor, int scale, RoundingMode roundingMode) ;
RoundingMode源碼解析：
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.
*
* 遠離0的舍入模式。總是在非零的小數前增加數值。請注意，該舍入模式不會減小計算值的大小。
*
*<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>
*
* 舉個栗子：
* 輸入一個數字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入後的數字：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。在放棄的小數之前不遞增數值（即截斷）。請注意，舍入模式不會增加計算值的大小。
*
*<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>
*
* 舉個栗子：
* 輸入一個數字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入後的數字：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.
*
* 向正無窮大舍入。如果結果是正數，執行RoundingMode.UP；如果結果是負數，執行RoundingMode.DOWN。
* 請注意，這個舍入模式決不會減少計算值。
*
*<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>
*
* 舉個栗子：
* 輸入一個數字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入後的數字：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.
*
* 向負無窮大舍入。如果結果是正數，執行RoundingMode.DOWN；如果結果是負數，執行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>
*
* 舉個栗子：
* 輸入一個數字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入後的數字：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.
*
* 向最鄰近的地方舍入。除非離左右兩邊的的數值是等距的，那麼就是用ROUND_UP模式。
* 如果捨棄的小數部分大於等於0.5，執行RoundingMode.UP，否則執行RoundingMode.DOWN。
* 請注意，這是學校常用的四捨五入舍入模式。
*
*<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>
*
* 舉個栗子：
* 輸入一個數字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入後的數字：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}.
*
* 向最鄰近的地方舍入。除非離左右兩邊的的數值是等距的，那麼就是用ROUND_DOWN模式。
* 如果捨棄的小數部分大於0.5，執行RoundingMode.UP，否則執行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>
*
* 舉個栗子：
* 輸入一個數字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入後的數字：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.
*
* 向最鄰近的地方舍入。除非離左右兩邊的的數值是等距的，那麼就向最鄰近的偶數舍入。
* 如果捨棄部分左邊的數字是奇數，執行RoundingMode.HALF_UP。如果是偶數，執行RoundingMode.HALF_DOWN。
* 請注意，這是一個舍入模式，當在一系列計算中重複應用時，可以統計學上最小化累積誤差。
* 它有時被稱爲"銀行家四捨五入"，主要用於美國。
* 這種舍入模式類似於Java中用於float和double算術的舍入策略。
*
*<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>
*
* 舉個栗子：
* 輸入一個數字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入後的數字：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.
*
* 舍入模式來斷言所請求的操作具有確切的結果，因此不需要舍入。
* 如果在產生不精確結果的操作上指定了舍入模式，則拋出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>
*
* 舉個栗子：
* 輸入一個數字：5.5 2.5 1.6 1.1 1.0 -1.0 -1.1 -1.6 -2.5 -5.5
* 舍入後的數字：異常 異常 異常 異常 1 -1 異常 異常 異常 異常
*/
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中對應於傳統整數舍入模式常量的RoundingMode對象。
*
* @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");
}
}
}