Generate Fake VCF file in kotlin

VcfGenerator.kt

fun main(args: Array<String>) {
    val charPool : List<Char> = ('a'..'z') + ('A'..'Z') + ('0'..'9')

    repeat(2) {
        val rand = Random()
        val stringBuilder = StringBuilder()
        stringBuilder.append("BEGIN:VCARD")
        stringBuilder.append("\n")
        stringBuilder.append("VERSION:3.0")
        stringBuilder.append("\n")
        val randomString = (1..6)
            .map { _ -> kotlin.random.Random.nextInt(0, charPool.size) }
            .map(charPool::get)
            .joinToString("");
        stringBuilder.append("N: $randomString; Cred;;;")
        stringBuilder.append("\n")
        stringBuilder.append("FN: $randomString Cred")
        stringBuilder.append("\n")

        val num1: Int = (rand.nextInt(7) + 1) * 100 + rand.nextInt(8) * 10 + rand.nextInt(8)
        val num2: Int = rand.nextInt(743)
        val num3: Int = rand.nextInt(10000)
        val df3 = DecimalFormat("000") // 3 zeros
        val df4 = DecimalFormat("0000") // 4 zeros
        val phoneNumber =
            "+91 " + df3.format(num1.toLong()) + "-" + df3.format(num2.toLong()) + "-" + df4.format(num3.toLong())
        stringBuilder.append("TEL;TYPE=CELL:$phoneNumber")
        stringBuilder.append("\n")
        stringBuilder.append("END:VCARD")
        println(stringBuilder.toString())
    }
}