DecimalFormat with RoundingMode.HALF_UP

Question

Having a simple code

import java.math.RoundingMode
import java.text.DecimalFormat
  
fun main(args: Array) {
  val f = DecimalFormat("#.##"         


        

Answer 1

Never ever use float or double if you want exact numbers to show up. If you round and want the rounding to happen on a solid base, you don't want float or double neither ;-)

Your sample using double would also give wrong results. Your sample using BigDecimal will give the results you expect. So... stick with BigDecimal if you want to be safe(r).

fun main(args: Array) {
  val f = DecimalFormat("#.##").apply { roundingMode = RoundingMode.HALF_UP }
  println(f.format(BigDecimal("-0.025")))
  println(f.format(BigDecimal("-0.015")))
  println(f.format(BigDecimal("-0.005")))
  println(f.format(BigDecimal("0.005")))
  println(f.format(BigDecimal("0.015")))
  println(f.format(BigDecimal("0.025")))
}