Question

To round a number I use the following code:

public static roundBd(BigDecimal bd){
  BigDecimal result1 = bd.setScale(0, RoundingMode.HALF_UP);
  return result1;
}

• Input 1.50 –> Output 2
• Input 1.499 –> Output 1

The first result is ok for me, but the second is not what I expected.
Even for 1.499 I’d like to have in output 2. (In details: first I’d like to round 1.499 to 1.50 then to 1.5 and finally to 2)

But….

BigDecimal bd = new BigDecimal("1.499");  // I'd like to round it to 2
BigDecimal result1 = bd.setScale(2, RoundingMode.HALF_UP); // result1 == 1.50
BigDecimal result2 = bd.setScale(1, RoundingMode.HALF_UP); // result2 == 1.5
BigDecimal result3 = bd.setScale(0, RoundingMode.HALF_UP); // result3 == 1

Answer 1

That’s not the way rounding works. HALF_UP means that if a number is exactly in the middle between the 2 closest available values (depending on the scale), it will be rounded up. Anything else is rounded to the closest value.

Extract from the javadoc:

Rounding mode to round towards “nearest neighbor” unless both neighbors are equidistant

To get to the behaviour you require, you could round successively although I’m not sure why you want such a behaviour:

BigDecimal bd = new BigDecimal("1.499");  // I'd like to round it to 2
BigDecimal result1 = bd.setScale(2, RoundingMode.HALF_UP); // result1 == 1.50
BigDecimal result2 = result1.setScale(0, RoundingMode.HALF_UP); // result2 == 2