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