IntelliJ IDEA: Why is readLine() expecting two user inputs instead of one using Kotlin?

Question

I wrote a simple program that takes the user's input from the console and then prints it. But when the user enters the input, it requests a second user input and only reads the second input.

Code:

fun main(args: Array<String>) {
    print("Enter text: ")
    val stringInput = readLine()!!
    println("Readed text: $stringInput")
}

Console:

> Task :MainKt.main()
Enter text: FirstInput
SecondInput
Disconnected from the target VM, address: 'localhost:37282', transport: 'socket'
Connected to the target VM, address: '127.0.0.1:37264', transport: 'socket'
Readed text: SecondInput

I'm using the latest version of IntelliJ IDEA. I don't know why this is happening. I'm using Windows.

score 3 · Accepted Answer · answered Dec 13 '20 at 23:44

3

This seems to be a bug in IntelliJ's internal console: see this ticket (found via this answer).

(The same issue also appears to be behind this question and this question.)

I don't know if it refers to the same problem, but this answer recommends changing the JRE options in the Edit Configurations menu, and then changing them back again.

answered Dec 13 '20 at 23:44

gidds

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After changing the JRE Options it works as expected. Thanks! – Lizzie Dec 14 '20 at 03:18

Simon Sultana · Answer 2 · 2020-12-13T22:59:52.117

-1

It might be because you are using "!!". Double bang (!!) or double exclamation operator or not-null assertion operator is used with variables that you are sure the value will be always be asserted (not null). If a value is null and one uses "!!", a one null pointer exception will be thrown. So, this operator is only used if we want to throw one exception always if any null value is found.

In your case:

fun main(args: Array<String>) {
    print("Enter text: ")

    val stringInput = readLine()
    println("Readed text: $stringInput")
}

You would want to use !! for example:

fun main(args: Array) {
   println("Enter text: ")
   val stringInput = null

   val inputLength = stringInput!!.length

   println("Length of the string is : $inputLength")

}

Since user input is null, the length of string would be null, hence The program will throw one kotlin.KotlinNullPointerException

edited Dec 13 '20 at 22:59

answered Dec 13 '20 at 22:12

Simon Sultana

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Please explain why `!!` is problematic – Marcin Orlowski Dec 13 '20 at 22:20
The problem persist even without the `!!` – Lizzie Dec 13 '20 at 22:56
@Lizzie I can think of the following possibilities at the moment: - Did you mistakenly declare 2 public static void main method? - Check if you have clicked on "Mute Breakpoints" button - Try maven clean followed by maven install – Simon Sultana Dec 13 '20 at 23:02
@Lizzie Click on debug again and in the right-hand corner, you should see a tool bar. There's an icon that looks like two red break points overlapping. Click on that. It will pop open a menu under any exception. Please ensure that Enabled, Suspend, All, Condition, log message to console and log evaluated expression are all checked. – Simon Sultana Dec 13 '20 at 23:05

IntelliJ IDEA: Why is readLine() expecting two user inputs instead of one using Kotlin?

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