Java Boolean.valueOf() equivalent in Kotlin?

Question

Is there a Kotlin equivalent of Boolean.valueOf() of java? The closest I found was .toBoolean().
But if the string is null .toBoolean() would create a NPE.

Did anyone come across this? Am I missing something understanding?

Answer 1

String.toBoolean

Returns true if the contents of this string is equal to the word "true", ignoring case, and false otherwise.

In Kotlin, a String is never null, so you don't have to check it. This returns a Boolean (true only if string value is 'true')

myString.toBoolean()

Now if you have a String? type and want a Boolean

myString?.toBoolean() ?: false

If you are ok with a Boolean? type returned

myString?.toBoolean()

Answer 2

It is, as already mentioned, .toBoolean().

It works pretty simple: if the value of a String is true, ignoring case, the returning value is true. In any other case, it's false. Which means, if the string isn't a boolean, it will return false.

Kotlin essentially has two variations of types: Any and Any?. Any can of course be absolutely any class, or referring to the actual class Any.

toBoolean requires a String, which means a non-null String. It's pretty basic:

val someString = "true"
val parsedBool = someString.toBoolean()

It gets slightly more complicated if you have nullable types. As I mentioned, toBoolean requires a String. A String? != String in these cases.

So, if you have a nullable type, you can use the safe call and elvis operator

val someString: String? = TODO()
val parsedBool = someString?.toBoolean() ?: false

Or, if you can live with a nullable boolean, you don't need the elvis operator. But if the String is null, so will the boolean be.

Just an explanation of the above:

someString?.//If something != null
    toBoolean() // Call toBoolean
    ?: false // Else, use false

Also, you can't compile a program that uses toBoolean on a nullable reference. The compiler blocks it.

---

And finally, for reference, the method declaration:

/**
 * Returns `true` if the contents of this string is equal to the word "true", ignoring case, and `false` otherwise.
 */
@kotlin.internal.InlineOnly
public actual inline fun String.toBoolean(): Boolean = java.lang.Boolean.parseBoolean(this)

Answer 3

You should know if it is null before the call, because you are either dealing with a String or a String?. ? is the suffix that Kotlin uses to designate nullable types.

If you have a String, then you should be able to use toBoolean().

If you have a String? — and so you may have a value or you may have null — you could use a null-safe call plus the Elvis operator to specify what value you want if the String? is null:

val foo: String? = "true"
val bar: String? = null

println(foo?.toBoolean())
println(bar?.toBoolean() ?: false)

This prints:

true
false

bar?.toBoolean() evaluates to null, and null ?: false evaluates to false.