How to convert String to Int in Kotlin?

Question

I am working on a console application in Kotlin where I accept multiple arguments in main() function

fun main(args: Array) {
    /         


        

Answer 1

Actually, there are several ways:

Given:

var numberString : String = "numberString" 
// number is the int value of numberString (if any)
var defaultValue : Int    = defaultValue

Then we have:

+—————————————————————————————————————————————+——————————+———————————————————————+
| numberString is a valid number ?            |  true    | false                 |
+—————————————————————————————————————————————+——————————+———————————————————————+
| numberString.toInt()                        |  number  | NumberFormatException |
+—————————————————————————————————————————————+——————————+———————————————————————+
| numberString.toIntOrNull()                  |  number  | null                  |
+—————————————————————————————————————————————+——————————+———————————————————————+
| numberString.toIntOrNull() ?: defaultValue  |  number  | defaultValue          |
+—————————————————————————————————————————————+——————————+———————————————————————+

Answer 2

val i = "42".toIntOrNull()

Keep in mind that the result is nullable as the name suggests.

Answer 3

fun getIntValueFromString(value : String): Int {
    var returnValue = ""
    value.forEach {
        val item = it.toString().toIntOrNull()
        if(item is Int){
            returnValue += item.toString()
        }

    }
    return returnValue.toInt()

}

Answer 4

I use this util function:

fun safeInt(text: String, fallback: Int): Int {
    return text.toIntOrNull() ?: fallback
}

Answer 5

As suggested above, use toIntOrNull().

Parses the string as an [Int] number and returns the result or null if the string is not a valid representation of a number.

val a: Int? = "11".toIntOrNull()   // 11
val b: Int? = "-11".toIntOrNull()  // -11
val c: Int? = "11.7".toIntOrNull() // null
val d: Int? = "11.0".toIntOrNull() // null
val e: Int? = "abc".toIntOrNull()  // null
val f: Int? = null?.toIntOrNull()  // null

Answer 6

You could call toInt() on your String instances:

fun main(args: Array<String>) {
    for (str in args) {
        try {
            val parsedInt = str.toInt()
            println("The parsed int is $parsedInt")
        } catch (nfe: NumberFormatException) {
            // not a valid int
        }
    }
}

Or toIntOrNull() as an alternative:

for (str in args) {
    val parsedInt = str.toIntOrNull()
    if (parsedInt != null) {
        println("The parsed int is $parsedInt")
    } else {
        // not a valid int
    }
}

If you don't care about the invalid values, then you could combine toIntOrNull() with the safe call operator and a scope function, for example:

for (str in args) {
    str.toIntOrNull()?.let {
        println("The parsed int is $it")
    }
}