rounding .5 down in java

Question

How can you implement a rounding function which will round all numbers as usual except 0.5 or any odd multiple of it down to the nearest integer?

For example:

• 2.899 is to be rounded up to 3.0
• 2.332 is to be rounded down to 2.0
• 2.5 is also to be rounded down to 2.0 (and NOT 3.0)

Answer 1

You can use BigDecimal as follows:

public static double roundHalfDown(double d) {
    return new BigDecimal(d)
            .setScale(0, RoundingMode.HALF_DOWN)
            .doubleValue();
}

Example:

for (double d : new double[] { 2.889, 2.332, 2.5 }) {
    System.out.printf("%.2f  ->  %.2f%n", d, roundHalfDown(d));
}

Output:

2.89  ->  3.00
2.33  ->  2.00
2.50  ->  2.00