BigDecimal 舍入模式（Rounding mode）介绍

我们在使用Java中的高精度浮点数时，有时根据实际需求需要对小数的舍入模式进行改变(默认为四舍五入方式)。下面对几种舍入模式进行介绍：

*ROUND_CEILING*Rounding mode to round towards positive infinity. 向正无穷方向舍入 *ROUND_DOWN*Rounding mode to round towards zero. 向零方向舍入 *ROUND_FLOOR* Rounding mode to round towards negative infinity. 向负无穷方向舍入 *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 *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* *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 *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 *ROUND_UP* Rounding mode to round away from zero. 向远离0的方向舍入

示例用法：

BigDecimal a = new BigDecimal("1.123141241");BigDecimal b = new BigDecimal("0.1243521");BigDecimal c = a.divide(b,new TextContent(20,RoundingMode.ROUND_HALF_UP));//TextContent表示两者相除后结果的数学环境，第一个参数用来表示结果的小数位数，第二个参数即用来指定相应的舍入模式