BigDecimal使用3--保留指定小数位API

BigDecimal保留小数位数之栗子

BigDecimal result = new BigDecimal("0.055");
        System.out.println(result);//0.055
        
        result.setScale(2, BigDecimal.ROUND_HALF_UP);
        System.out.println(result);//0.06
        
        result.setScale(2, BigDecimal.ROUND_HALF_DOWN);
        System.out.println(result);//0.05
        
        result.setScale(2, BigDecimal.ROUND_CEILING);
        System.out.println(result);//0.06
        
        result.setScale(2, BigDecimal.ROUND_FLOOR);
        System.out.println(result);//0.05
        
        result.setScale(2, BigDecimal.ROUND_DOWN);
        System.out.println(result);//0.05
        
        result.setScale(2, BigDecimal.ROUND_UP);
        System.out.println(result);//0.05
        
        result = result.setScale(BigDecimal.ROUND_UNNECESSARY);//计算结果位精确类型，不需要保留小数位
        System.out.println(result);//0.05
        
        result = result.setScale(2);//保留2位小数（默认使用四舍五入）
        System.out.println(result);//0.05

参数定义

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