how can i read strings from multiple lines and print them out respectively?

Question

class MusicPlayer {
    private var songs: Array<String> = arrayOf("")    
    var index = songs.size

    fun add(track: String) {
        songs[index-1] = track
    }
    fun show() {
        for (item in songs) {
            println(item)
        }
    }
}

fun main(args: Array<String>) {
    val m = MusicPlayer()
    
    while(true) {
        var input = readLine()!!
        if(input == "stop") {
            break
        }
        m.add(input)
    }
    m.show()
}

my inputs are

>Purple Haze
>Under Pressure
>Walk This Way
>stop

expected output

>Purple Haze
>Under Pressure
>Walk This Way
>Playing Purple Haze

but what i get is

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index -1 out of bounds for length 0

Answer 1

add function in MusicPlayer class has no sense. First, imagine first three iterations. We call add method 3 times, like this:

m.add("song1")
m.add("song2")
m.add("song3")

In MusicPlayer it will look like this: (You are not modifying "index" variable anywhere, so...)

// index = 1
// songs[index - 1] = songs[1 - 1] = songs[0]

//first add
songs[0] = "song1"

//second add
songs[0] = "song2"

//third add
songs[0] = "song3"

---

Second, the size of the array is not dynamic. If you declare an array with size = 1, its size will always be 1. You can't do something like that

private var songs: Array<Stirng> = arrayOf("")
songs[2] = "exampleText" //ArrayIndexOutOfBoundsException

Array reserved memory for just 1 element. There are ways to deal with it, but in your example, I recommeng you to use ArraysList or MutableList (Almost the same). Such collection allows you to freely modify it's size/length.

Your MusicPlayer with ArrayList would look like this

    private var songs: ArrayList<String> = ArrayList()

    fun add(track: String) {
        songs.add(track)
    }
    fun show() {
        for (item in songs) {
            println(item)
        }
    }