Round Double to 1 decimal place kotlin: from 0.044999 to 0.1

Finally I did what Andy Turner suggested, rounded to 3 decimals, then to 2 and then to 1:

Answer 1:

val number:Double = 0.0449999
val number3digits:Double = String.format("%.3f", number).toDouble()
val number2digits:Double = String.format("%.2f", number3digits).toDouble()
val solution:Double = String.format("%.1f", number2digits).toDouble()

Answer 2:

val number:Double = 0.0449999
val number3digits:Double = Math.round(number * 1000.0) / 1000.0
val number2digits:Double = Math.round(number3digits * 100.0) / 100.0
val solution:Double = Math.round(number2digits * 10.0) / 10.0

Result:

0.045 → 0.05 → 0.1

Note: I know it is not how it should work but sometimes you need to round up taking into account all decimals for some special cases so maybe someone finds this useful.

I know some of the above solutions work perfectly but I want to add another solution that uses ceil and floor concept, which I think is optimized for all the cases.

If you want the highest value of the 2 digits after decimal use below code.

import java.math.BigDecimal 
import java.math.RoundingMode
import java.text.DecimalFormat

here, 1.45678 = 1.46

fun roundOffDecimal(number: Double): Double? {
    val df = DecimalFormat("#.##")
    df.roundingMode = RoundingMode.CEILING
    return df.format(number).toDouble()
}

If you want the lowest value of the 2 digits after decimal use below code.

here, 1.45678 = 1.45

fun roundOffDecimal(number: Double): Double? {
    val df = DecimalFormat("#.##")
    df.roundingMode = RoundingMode.FLOOR
    return df.format(number).toDouble()
}

Here a list of all available flags: CEILING, DOWN, FLOOR, HALF_DOWN, HALF_EVEN, HALF_UP, UNNECESSARY, UP

The detailed information is given in docs