So I have this Java code:
String values = input.nextLine();
String[] longs = values.split(" ");
Which splits the string input into a string array.
I try it in Kotlin
var input: String? = readLine()
var ints: List<String>? = input.split(" ".toRegex())
and I get an error: "Only safe (?.) or non-null asserted (!!.) calls are allowed on a nullable receiver of the the type String?"
I am new to Kotlin and would like some clarity on how to do this. Thank you!
If you have a look at readLine() it reveals that it might return null:
/**
* Reads a line of input from the standard input stream.
*
* @return the line read or `null` if the input stream is redirected to a file and the end of file has been reached.
*/
public fun readLine(): String? = stdin.readLine()
Therefore it's not safe to call split on its result, you have to handle the null case, e.g. as follows:
val input: String? = readLine()
val ints: List<String>? = input?.split(" ".toRegex())
Other alternatives and further information can be found here.
!! is almost never the answer. Propagating nullability gives you a chance to handle any unexpected errors gracefully.Look, you code is almost right, just missed the !! this ensure that the string should not be empty (it will throw a error). You code should be like this:
val input: String? = readLine()
var ints: List<String>? = input!!.split(" ".toRegex())
Note that I just added !! operator and change var to val on line 1, because your input should not be changed (it was given by the user).
String! which means "could be either a String? or a String") to a definite non-null type!! with the safe navigation operator ?., because ints is a nullable type and ?. will return null if input is null, whereas !! will throw an exception if input is null, never resulting in a null being assigned to ints