金额的数据类型是BigDecimal
通过BigDecimal的divide方法进行除法时当不整除，出现无限循环小数时，就会抛异常的，异常如下：java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result. at java.math.BigDecimal.divide(Unknown Source)
应用场景：一批中供客户的单价是1000元/年，如果按月计算的话1000/12=83.3333333333....
解决之道：就是给divide设置精确的小数点divide(xxxxx,2, BigDecimal.ROUND_HALF_EVEN)
在 java中， 四舍五入通过 BigDecimal 来实现。一定要注意：BigDecimal is Immutable。也就是跟String一样，对前一个的修改，比如setScale(), add（）等都会返回一个新的ＢigDecimal.四舍五入舍入模式是 BigDecimal.ROUND_HALF_UP
BigDecimal定义了一下舍入模式，只有在作除法运算或四舍五入时才用到舍入模式，下面简单介绍，详细请查阅J2se API文档
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static int |
ROUND_CEILING
Rounding mode to round towards positive infinity.
向正无穷方向舍入 |
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static int |
ROUND_DOWN
Rounding mode to round towards zero.
向零方向舍入 |
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static int |
ROUND_FLOOR
Rounding mode to round towards negative infinity.
向负无穷方向舍入 |
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static int |
ROUND_HALF_DOWN
Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round down.
向（距离）最近的一边舍入，除非两边（的距离）是相等,如果是这样，向下舍入, 例如1.55 保留一位小数结果为1.5 |
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static int |
ROUND_HALF_EVEN
Rounding mode to round towards the "nearest neighbor" unless both neighbors are equidistant, in which case, round towards the even neighbor.
向（距离）最近的一边舍入，除非两边（的距离）是相等,如果是这样，如果保留位数是奇数，使用ROUND_HALF_UP ，如果是偶数，使用ROUND_HALF_DOWN |
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static int |
ROUND_HALF_UP
Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round up.
向（距离）最近的一边舍入，除非两边（的距离）是相等,如果是这样，向上舍入, 1.55保留一位小数结果为1.6 |
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static int |
ROUND_UNNECESSARY
Rounding mode to assert that the requested operation has an exact result, hence no rounding is necessary.
计算结果是精确的，不需要舍入模式 |
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static int |
ROUND_UP
Rounding mode to round away from zero.
向远离0的方向舍入 | |
