BigDecimal rounding mode issue

Question

I need to get these results using BigDecimal roundingmode.xxx and setScale(2) :

(5.789).setScale(2, RoundingMode.xxx) = 5.79

(2.894).setScale(2, RoundingMode.xxx) = 2.89

(2.895).setScale(2, RoundingMode.xxx) = 2.89

Where RoundingMode.xxx has to be same for the three given values.

Ive tried all combinations but with no success and Microsoft Excel set the three results with success.

Answer 1

The problem is when I was multiplying two BigDecimal numbers I got a big result. After that I used setScale(2, HalfDown) but did not get the desired result.

The wrong result

"2.89500004313886165618896484375".setScale(2, BigDecimal.ROUND_HALF_DOWN);

I need 2.89 and the wrong result was 2.90

Using .round(new MathContext(2)) I got it :

 "2.89500004313886165618896484375".round(new MathContext(2));

The right result is 2.89

Answer 2

You could use ROUND_HALF_DOWN:

Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round down. Behaves as for ROUND_UP if the discarded fraction is > 0.5; otherwise, behaves as for ROUND_DOWN.

For your input:

static void roundTo(BigDecimal input)
{
    BigDecimal output = input.setScale(2, BigDecimal.ROUND_HALF_DOWN);
    System.out.println(input + " => " + output);
}

roundTo(new BigDecimal("5.789"));
roundTo(new BigDecimal("2.894"));
roundTo(new BigDecimal("2.895"));

This would produce:

5.789 => 5.79
2.894 => 2.89
2.895 => 2.89

---

EDIT: As per your comments, the following might work for you:

BigDecimal output = input.setScale(3, BigDecimal.ROUND_HALF_DOWN).setScale(2, BigDecimal.ROUND_HALF_DOWN);

Answer 3

You are looking for RoundingMode.HALF_DOWN

Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round down. Behaves as for RoundingMode.UP if the discarded fraction is > 0.5; otherwise, behaves as for RoundingMode.DOWN.

Example:

public static void main(String args []){

  System.out.println(new BigDecimal("5.789").setScale(2, RoundingMode.HALF_DOWN));
  System.out.println(new BigDecimal("2.894").setScale(2, RoundingMode.HALF_DOWN));
  System.out.println(new BigDecimal("2.895").setScale(2, RoundingMode.HALF_DOWN));

}

Output

5.79
2.89
2.89