Kotlin cast string to int

How to convert Any to Int in Kotlin

What do you mean by «try to cast directly to Int»? I don’t see the code for that here. Are you simply trying to do: value.toInt() ? Or are you attempting an explicit cast: (Integer)value ?

From the example, it seems like that the var called value sometimes contains a String which happens contain an Int. If this is the case, you have to first cast it to String, and then parse it, for example, with the toInt method, as you already did.

If you do value as? Int , then the result will be safe cast to Int? (if value is Int the result will be the value, otherwise it will be null .

4 Answers 4

The problem is that you were attempting to cast directly from a String to an Int with value as Int .

This isn’t working because, as the exception is telling you, value contains a String, and a String cannot be coerced into an Int. The fact that this String represents an integer doesn’t matter, as it would need to be parsed into an Int. That precisely is what the toInt() method does.

The reason you must cast to a String first is because toInt() is an extension method on String, and value is of type Any? . This means that you can’t call toInt() directly on value because it doesn’t know that it contains a String at compile time, even though it does at runtime. If you wanted to skip this step, you could also use smart casts by checking the type first:

You can find a bit more info on smart casts and other Kotlin type casting here: https://kotlinlang.org/docs/reference/typecasts.html#smart-casts

This also may be pointing to an underlying design problem. You expect that this will sometimes contain an Int, but as we can see here whatever is setting this value in your model is setting it to a String containing that number. Do you expect this value to truly be able to contain many different types, or are you only expect Int and String? If the latter, then it would possibly be a better design decision to make this a String rather than an Any? . That would prevent unexpected/unhandled types from being provided, and make the model less ambiguous to anyone looking at or using it.

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Kotlin – String to Integer – String.toInt()

To convert a string to integer in Kotlin, use String.toInt() or Integer.parseInt() method. If the string can be converted to a valid integer, either of the methods returns int value.

You may need to convert a string to integer in scenarios like: extracting numbers from string messages and perform some arithmetic operations on them; you receive a value as string from outside your program, but you are treating it as an integer in your application; etc.

In this tutorial, we shall learn different ways of how to convert a string to integer and different scenarios where we may need to use this conversion.

Syntax

The syntax of String.toInt() is given below.

String.toInt() returns int value if conversion is successful. Else, it throws java.lang.NumberFormatException.

The syntax of Integer.parseInt() is given below.

Integer.parseInt() function takes the string as argument and returns int value if conversion is successful. Else, it throws java.lang.NumberFormatException same as that of String.toInt().

Examples

1. Convert String to Integer using String.toInt()

In this example, we shall first initialize a string. Secondly we call toInt() on the string and store the returned int value. You can use this int value as per your requirement, but in this example, we are just printing it.

/** * Kotlin - Convert Sting to Integer */ fun main(args: Array) < //a string val str = "241" //convert string to integer val num = str.toInt() print(num+10) >

Run this Kotlin program. Just to prove that it is an int, we are adding a value of 10 to it and printing the result.

2. Convert String to Integer using Integer.parseInt()

In this example, we shall first initialize a string. Secondly we call Integer.parseInt() with the string as arguemnt the string and store the returned int value.

/** * Kotlin - Convert Sting to Integer */ fun main(args: Array) < //a string val str = "241" //convert string to integer val num = Integer.parseInt(str) print(num+10) >

Run this Kotlin program. Like in the previous example, we are adding a value of 10 to the integer and printing the result.

3. Convert String to Int – Negative Scenario

In this example, we shall try to convert a string to integer, where the string, as a whole, does not represent a valid integer. Let us see what happens. Certainly, str.toInt() throws an exception.

/** * Kotlin - Convert Sting to Integer */ fun main(args: Array) < //a string val str = "241a" //convert string to integer val num = str.toInt() print(num+10) >

Run this Kotlin program, and you will get the following output.

Exception in thread "main" java.lang.NumberFormatException: For input string: "241a" at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.base/java.lang.Integer.parseInt(Integer.java:652) at java.base/java.lang.Integer.parseInt(Integer.java:770) at KotlinStringToIntegerKt.main(KotlinStringToInteger.kt:8)

Yeah, as we have already mentioned, an Exception occurred. Specifically it is java.lang.NumberFormatException.

Conclusion

In this Kotlin Tutorial, we learned how to convert a string to integer using different methods.

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How to cast String into Int and Long?

You can just use toInt , toLong , and similar conversion extensions.

val i: Int = str.toInt() val l: Long = str.toLong() 

There’s also toIntOrNull , etc. in case your strings might not be valid numbers:

val i: Int? = str.toIntOrNull() 

fun String.toIntOrElse(defaultValue: Int) :Int = toIntOrNull() ?: defaultValue usage: val i = str.toIntOrElse(0)

Kotlin has extension methods for String class that do the same but more elegantly.

Note that you can write extension methods yourself as well.

Kotlin define extension function in StringNumberConversions.kt like toInt, toLong etc. These functions internally invoke standard java function like java.lang.Integer.parseInt(. ) or java.lang.Long.parseLong(. )

These are Extension methods available for Strings to parse in KOTLIN:

 str.toBoolean() str.toInt() str.toLong() str.toFloat() str.toDouble() str.toByte() str.toShort() 

val str = "" val quotaInteger = str.toDouble().toInt() 

cos sometime end give us like «123.22», if we use toInt(), it will throw out NumberFormatException

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How to Convert a String to Integer in Kotlin

Kotlin is a powerful, statically-typed language that has been gaining popularity in the development world. It’s known for its concise syntax and type-safety, which makes it ideal for developing applications quickly. It also provides a wide range of features that make it a great choice for developers. One of the most common tasks when working with Kotlin is converting a String to an Integer. This tutorial will explain how to accomplish this task in Kotlin.

What is an Integer

Before we dive into the details of how to convert a String to an Integer in Kotlin, it’s important to understand what an Integer is. An Integer is a numerical data type that can store whole numbers (positive, negative, or zero). Integers are represented in Kotlin as Int data types, which are 32-bit signed two’s complement integers.

Converting a String to an Integer in Kotlin

The easiest way to convert a String to an Integer in Kotlin is to use the toInt() function. This function takes a String as an argument and returns an Int value. The toInt() function can be used in two ways:

// Convert a String to an Integer val intValue = "123".toInt() 

// Convert a String to an Integer, returning a nullable Int val intValue = "123".toIntOrNull() 

The toIntOrNull() function is useful when you’re not sure if the String can be successfully converted to an Integer. If the String can’t be converted, toIntOrNull() will return a null value instead of an exception.

Converting a String to an Integer in Kotlin with Exceptions

If you want to handle exceptions when converting a String to an Integer, you can use the toIntOrThrow() function. This function takes a lambda function as an argument, which will be called if the conversion fails. The lambda function should return a custom exception type, which will be thrown if the conversion fails.

Here’s an example of how to use the toIntOrThrow() function:

// Convert a String to an Integer, throwing a custom exception val intValue = "123".toIntOrThrow  throw IllegalArgumentException("String cannot be converted to an Integer") > 

Converting a String to an Integer with Regex

Kotlin also provides a way to convert a String to an Integer using regular expressions (regex). This approach is useful if you want to validate the String before converting it. For example, you might want to make sure that the String only contains numbers and no other characters.

Here’s an example of how to use regex to convert a String to an Integer:

// Convert a String to an Integer using regex val intValue = Regex("\\d+").find("123")?.value?.toInt() 

The find() method in the regex example will return a MatchResult object, which contains the matched substring. In this case, the matched substring is the number “123”. The value property on the MatchResult object will return the matched substring as a String , which can then be converted to an Integer using the toInt() function.

Conclusion

Converting a String to an Integer in Kotlin is a straightforward task that can be accomplished in several different ways. The most common approach is to use the toInt() method, which takes a String as an argument and returns an Int value. You can also use the toIntOrNull() and toIntOrThrow() functions to handle exceptions or validate the String using regex before converting it. No matter which approach you take, you should now have a better understanding of how to convert a String to an Integer in Kotlin.

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