Reputation: 1632

How to convert String to Int in Kotlin?

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

fun main(args: Array<String>) {
    // validation & String to Integer conversion
}

I want to check whether the String is a valid integer and convert the same or else I have to throw some exception.

How can I resolve this?

Upvotes: 124

Answers (12)

James Walton

Reputation: 81

If you actually have a String, call toInt() on it:

val myInt = myString.toInt()

Are you actually sure it's a String, though? If you're iterating over a single String, you don't get instances of String of length 1 (as you might expect if you're used to another language, ie, Python), but instances of Char, in which case you want to use digitToInt() instead:

val myInt = myChar.digitToInt()

Upvotes: 8

WOWOW

Reputation: 21

toInt()

You can call toInt() on a String to turn it into an Integer.

val number_int = str.toInt()

If it cannot be converted, it will throw a NumberFormatException error.

You could put it in a try-catch block:

try {
    val strVal = "IamNotanInteger"
    val intVal = strVal.toInt()
    println(intVal)
} catch (e: NumberFormatException) {
    println("This String is not convertible.")
}

toIntOrNull()

toIntOrNull() will also convert a String into an Integer, but it will return null instead of throwing an error.

fun main() {
    val strVal = "246b"
    val intVal = strVal.toIntOrNull()
    println(intVal) // null
}

Integer.parseInt()

Here’s how to use the parseInt() method to convert Kotlin String to Int.

fun main() {
    val strVal = "246"
    val intVal = Integer.parseInt(strVal)
    println(intVal) // 246
}

Non-Decimal System

You can pass a radix into the toInt() and toIntOrNull() methods:

fun main() {
    val base16String = "3F"
    val base16Int = base16String.toInt(16)
    // String Interpolation
    println("$base16Int") // 63 (If I did the maths correct...)
}

Useful Links

Upvotes: 2

Hoa Nguyen

Reputation: 14560

Actually, there are several ways:

Given:

// aString is the string that we want to convert to number    
// defaultValue is the backup value (integer) we'll have in case of conversion failed

var aString: String = "aString"     
var defaultValue : Int    = defaultValue

Then we have:

Operation	Successful operation	Unsuccessful Operation
aString.toInt()	Numeric value	NumberFormatException
aString.toIntOrNull()	Numeric value	null
aString.toIntOrNull() ?: defaultValue	Numeric value	defaultValue

If aString is a valid integer, then we will get is numeric value, else, based on the function used, see a result in column Unsuccessful Operation.

Upvotes: 39

Deepak Kumar Yadav

Reputation: 11

You can Direct Change by using readLine()!!.toInt()

Example:

fun main(){

    print("Enter the radius = ")
    var r1 = readLine()!!.toInt()
    var area = (3.14*r1*r1)
    println("Area is $area")

}

Upvotes: 1

Ghayas

Reputation: 1334

In Kotlin:

Simply do that

val abc = try {stringNumber.toInt()}catch (e:Exception){0}

In catch block you can set default value for any case string is not converted to "Int".

Upvotes: 5

Djalal Messerhi

Reputation: 11

add (?) before fun toInt()

val number_int = str?.toInt()

Upvotes: 1

CoolMind

Reputation: 28865

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

Upvotes: 7

Goran Horia Mihail

Reputation: 3645

I use this util function:

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

Upvotes: 4

therealsanaullah

Reputation: 1

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

    }
    return returnValue.toInt()

}

Upvotes: 0

Grzegorz Piwowarek

Reputation: 13863

val i = "42".toIntOrNull()

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

Upvotes: 20

earthw0rmjim

Reputation: 19427

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")
    }
}

Upvotes: 139

leetwinski

Reputation: 17849

i would go with something like this.

import java.util.*

fun String?.asOptionalInt() = Optional.ofNullable(this).map { it.toIntOrNull() }

fun main(args: Array<String>) {
    val intArgs = args.map {
        it.asOptionalInt().orElseThrow {
            IllegalArgumentException("cannot parse to int $it")
        }
    }

    println(intArgs)
}

this is quite a nice way to do this, without introducing unsafe nullable values.