public class test1_format {

    public static void main(String[] args) {
        BigDecimal decimal = new BigDecimal("1.12345");
        System.out.println(decimal);
        BigDecimal setScale = decimal.setScale(4,BigDecimal.ROUND_HALF_DOWN);
        System.out.println(setScale);
        
        BigDecimal setScale1 
 
= decimal.setScale(4,BigDecimal.ROUND_HALF_UP);
        System.out.println(setScale1);
    }
}

引數定義

ROUND_CEILING
Rounding mode to round towards positive infinity.
向正無窮方向舍入

ROUND_DOWN
Rounding mode to round towards zero.
向零方向舍入

ROUND_FLOOR
Rounding mode to round towards negative infinity.
向負無窮方向舍入

ROUND_HALF_DOWN

Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round down.
向（距離）最近的一邊舍入，除非兩邊（的距離）是相等,如果是這樣，向下舍入, 例如1.55 保留一位小數結果為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（距離）最近的一邊舍入，除非兩邊（的距離）是相等,如果是這樣，如果保留位數是奇數，使用ROUND_HALF_UP ，如果是偶數，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（距離）最近的一邊舍入，除非兩邊（的距離）是相等,如果是這樣，向上舍入, 1.55保留一位小數結果為1.6


ROUND_UNNECESSARY
Rounding mode to assert that the requested operation has an exact result, hence no rounding is necessary.
計算結果是精確的，不需要舍入模式


ROUND_UP
Rounding mode to round away from zero.
向遠離0的方向舍入