Efficient BigDecimal round Up and down to two decimals

Question

In java am trying to find an efficient way to round a BigDecimal to two decimals, Up or Down based on a condition.

 IF condition true then:
    12.390 ---> 12.39
    12.391 ---> 12.40
    12.395 ---> 12.40
    12.399 ---> 12.40

 If condition false then:
    12.390 ---> 12.39
    12.391 ---> 12.39
    12.395 ---> 12.39
    12.399 ---> 12.39

What is the most efficient way to accomplish this?

Answer 1

public static BigDecimal round(BigDecimal d, int scale, boolean roundUp) {
  int mode = (roundUp) ? BigDecimal.ROUND_UP : BigDecimal.ROUND_DOWN;
  return d.setScale(scale, mode);
}
round(new BigDecimal("12.390"), 2, true); // => 12.39
round(new BigDecimal("12.391"), 2, true); // => 12.40
round(new BigDecimal("12.391"), 2, false); // => 12.39
round(new BigDecimal("12.399"), 2, false); // => 12.39

Answer 2

num = num.setScale(condition ? RoundingMode.UP : RoundingMode.DOWN);

But note that your spec is not entirely clear when it comes to negative numbers. Take a look at the various rounding modes in the API doc and see what exactly you need.