1   public class test1_format {

2   public static void main(String[] args) {

3   BigDecimal decimal = new BigDecimal("1.12345");

4   System.out.println(decimal);

5   BigDecimal setScale = decimal.setScale(4,BigDecimal.ROUND_HALF_DOWN);

6   System.out.println(setScale);

7

8   BigDecimal setScale1 = decimal.setScale(4,BigDecimal.ROUND_HALF_UP);

9   System.out.println(setScale1);

10  }

11  }

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