How to Convert String to Int, Float, Double, Long in Kotlin

This tutorial explains some of the useful methods about how to convert String to Int, Float, Double, Long in Kotlin/Android.

Let’s get started.

Kotlin Convert String to Int Example

We are going to test the following examples:

The toInt() method helps to parse the string to an Int numerical value. However, It throws a NumberFormatException exception if it finds the string is not a correct representation of a number value.

The toIntOrNull() method parses the string to an Int and returns null if it finds string doesn’t belong valid numerical representation.

fun main() {
   var str:String = "20"
   var num:Int = str.toInt()
   print(num) 
   // output: 20
    
    
   val strA = "30.1"
   val numA: Int? = strA.toInt()
   println(strA) 
   // output: Exception in thread "main" java.lang.NumberFormatException: For input string: "30.1"
 
   val int: Int? = strA.toIntOrNull()
   println(int)
   // output: null
    
   val strB = "555"
   val intB: Int? = strB.toInt(6)
   println(intB)
   // output: 215       
}

Convert String to Float in Kotlin/Android

Here are the example that we are about to explore:

The toFloat() method converts the string to a Float, It throws the NumberFormatException exception when the string is not a legitimate representation of a Float.

The toFloatOrNull() method parses the string to a Float, It returns a null value when it finds the string is not a valid representation of a Float.

fun main() {
  val floatStr1 = "234.12f";
  val floatVal1: Float? = floatStr1.toFloat()
  println(floatStr1)
  // output: 234.12f
	
  
  val floatStr2 = "C234.345";
  val floatVal2: Float? = floatStr2.toFloat()
  // output: Exception in thread "main" java.lang.NumberFormatException: For input string: "C234.345"
      
  val floatStr3 = "A23.456";    
  val floatStr4: Float? = floatStr3.toFloatOrNull()
  println(floatStr4)
  // output: null
}

Convert String to Double in Kotlin

We will explore the following examples:

The toDouble() method converts the string to a Double, It returns NumberFormatException if it sees the string is not a valid representation of a Double.

The toDoubleOrNull() method parses the string to a Double, It returns a null value if it finds the string is not a valid representation of a Double.

fun main() {
  val doubleStr1 = "2.123456789"
  val doubleVal1: Double? = doubleStr1.toDouble()
  println(doubleVal1)
  // output: 2.123456789
  
	
  val doubleStr2 = "C2.12";
  val doubleVal2: Double? = doubleStr2.toDouble()
  println(doubleVal2)
  // output: Exception in thread "main" java.lang.NumberFormatException: For input string: "C2.12"
	
  val doubleStr3 = "X1.007";
  val doubleVal3: Double? = doubleStr3.toDoubleOrNull()
  println(doubleVal3)
  // output: null
}

Convert String to Long in Kotlin

We are about to understand the following Kotlin methods with examples:

The toLong() method parses the string to a Long, and It returns a NumberFormatException when it finds the string is not a valid representation of a Long.

The toLongOrNull() method converts the string to a Long, It returns a null value when it finds the string is not a valid representation of a Long.

The toLong(10) method parses the string as a “Long === 10” number and returns the result. It throws NumberFormatException if it sees string is not a valid representation of a number.

It even throws an IllegalArgumentException when it finds the “radix” is not a valid radix for the string to number conversion.

fun main() {
  val longStr1 = "31000000"
  val longVal1: Long? = longStr1.toLong()
  println(longVal1)
  // output: 31000000
	
    
  val longStr2 = "21.21";
  val longVal2: Long? = longStr2.toLong()
  // output: Exception in thread "main" java.lang.NumberFormatException: For input string: "21.21"
	
  val longStr3 = "11.11";    
  val longVal3: Long? = longStr3.toLongOrNull()
  println(longVal3)
  // output: null
	
    
  val longStr4 = "AAA"
  val longVal4: Long? = longStr4.toLong(14)
  println(longVal4)
  // output: 2110
  
  val longStr5 = "AAA"
  val longVal5: Long? = longStr5.toLong(8)
  println(longVal5)
  // output: Exception in thread "main" java.lang.NumberFormatException: For input string: "AAA"
	
    
  val longStr6 = ""
  val longVal6: Long? = longStr6.toLongOrNull(8)
  println(longVal6)
  // output: null
}

Conclusion

So, that was it. In this tutorial, we have come across the prevalent programming concepts converting String to a Number. We have learned how to work with Kotlin String type conversion methods. On top of that, we successfully converted String to Int, Float, Double, Long in Kotlin/Android.

We barely scratched the surface; however, if you want to dig deep, then you should check out the Types in Kotlin and Kotlin API.

Happy Coding!

Reference: Bezkoder