BigDecimal 保留小数位

Bigdecimal记录

    BigDecimal decimal = new BigDecimal("1.55");

    BigDecimal round_ceiling = decimal.setScale(1,BigDecimal.ROUND_CEILING);
    System.out.println("round_ceiling = " +  round_ceiling + "n");

    BigDecimal round_down = decimal.setScale(1,BigDecimal.ROUND_DOWN);
    System.out.println("round_down = " + round_down + "n");

    BigDecimal round_floor = decimal.setScale(1,BigDecimal.ROUND_FLOOR);
    System.out.println("round_floor = " + round_floor + "n");

    BigDecimal round_half_down = decimal.setScale(1,BigDecimal.ROUND_HALF_DOWN);
    System.out.println("round_half_down = " + round_half_down + "n" );

    BigDecimal round_half_up = decimal.setScale(1,BigDecimal.ROUND_HALF_UP);
    System.out.println("round_half_up = " + round_half_up + "n");

    BigDecimal round_half_even = decimal.setScale(1,BigDecimal.ROUND_HALF_EVEN);
    System.out.println("round_half_even = " + round_half_even + "n" );

    BigDecimal round_unnecessary = decimal.setScale(2,BigDecimal.ROUND_UNNECESSARY);
    System.out.println("round_unnecessary = " + round_unnecessary + "n" );

    BigDecimal round_up = decimal.setScale(1,BigDecimal.ROUND_UP);
    System.out.println("round_up = " + round_up + "n" );

打印结果：

round_ceiling = 1.6

round_down = 1.5

round_floor = 1.5

round_half_down = 1.5

round_half_up = 1.6

round_half_even = 1.6

round_unnecessary = 1.55

round_up = 1.6

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

最后

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