用readLine（）方法拆分Kotlin字符串

Question

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!

Answer 1

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, eg as follows:

val input: String? = readLine()
val ints: List<String>? = input?.split(" ".toRegex())

Other alternatives and further information can be found here .

Answer 2

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).